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• Deleting a node from linked list in C

  - by LuckySlevin

  My problem is deleting a node from linked list. I have two structs : typedef struct inner_list { int count; char word[100]; inner_list*next; } inner_list; typedef struct outer_list { char word [100]; inner_list * head; int count; outer_list * next; } outer_list; My problem is in deleting a node from outer_list linked list. For example when user entered aaa to delete, delete function should find the node with outer_list->word = aaa and delete this node and reconnect the list again. I tried the below code to do this. but After finding and deleting I'm losing the list. I don't know what's wrong. Please notice that outer_list have also a linked list of inner_list inside. void delnode(outer_list *head,char num[100]) { outer_list *temp, *m; temp=head; while(temp!=NULL) { if(strcmp(temp->word==num)==0) { if(temp==head) { head=temp->next; free(temp); return; } else { m->next=temp->next; free(temp); return; } }else { m=temp; temp= temp->next; } } printf(" ELEMENT %s NOT FOUND ", num); } What are your ideas about this?

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• verifying the signature of x509

  - by sid

  Hi All, While verifying the certificate I am getting EVP_F_EVP_PKEY_GET1_DH My Aim - Verify the certificate signature. I am having 2 certificates : 1. a CA certificate 2. certificate issued by CA. I extracted the 'RSA Public Key (key)' Modulus From CA Certificate using, pPublicKey = X509_get_pubkey(x509); buf_len = (size_t) BN_num_bytes (bn); key = (unsigned char *)malloc (buf_len); n = BN_bn2bin (bn, (unsigned char *) key); if (n != buf_len) LOG(ERROR," : key error\n"); if (key[0] & 0x80) LOG(DEBUG, "00\n"); Now, I have CA public key & CA key length and also having certificate issued by CA in buffer, buffer length & public key. To verify the signature, I have following code int iRet1, iRet2, iRet3, iReason; iRet1 = EVP_VerifyInit(&md_ctx, EVP_sha1()); iRet2 = EVP_VerifyUpdate(&md_ctx, buf, buflen); iRet3 = EVP_VerifyFinal(&md_ctx, (const unsigned char *)CAkey, CAkeyLen, pubkey); iReason = ERR_get_error(); if(ERR_GET_REASON(iReason) == EVP_F_EVP_PKEY_GET1_DH) { LOG(ERROR, "EVP_F_EVP_PKEY_GET1_DH\n"); } LOG(INFO,"EVP_VerifyInit returned %d : EVP_VerifyUpdate returned %d : EVP_VerifyFinal = %d \n", iRet1, iRet2, iRet3); EVP_MD_CTX_cleanup(&md_ctx); EVP_PKEY_free(pubkey); if (iRet3 != 1) { LOG(ERROR,"EVP_VerifyFinal() failed\n"); ret = -1; } LOG(INFO,"signature is valid\n"); I am unable to figure out What might went wrong??? Please if anybody faced same issues? What EVP_F_EVP_PKEY_GET1_DH Error means? Thanks in Advance - opensid

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• what does this attempted trojan horse code do?

  - by bstullkid

  It looks like this just sends a ping, but whats the point of that when you can just use ping? /* WARNING: this is someone's attempt at writing a malware trojan. Do not compile and *definitely* don't install. I added an exit as the first line to avoid mishaps - msw */ int main (int argc, char *argv[]) { exit(1); unsigned int pid = 0; char buffer[2]; char *args[] = { "/bin/ping", "-c", "5", NULL, NULL }; if (argc != 2) return 0; args[3] = strdup(argv[1]); for (;;) { gets(buffer); /* FTW */ if (buffer[0] == 0x6e) break; switch (pid = fork()) { case -1: printf("Error Forking\n"); exit(255); case 0: execvp(args[0], args); exit(1); default: break; } } return 255; }

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• cast operator to base class within a thin wrapper derived class

  - by miked

  I have a derived class that's a very thin wrapper around a base class. Basically, I have a class that has two ways that it can be compared depending on how you interpret it so I created a new class that derives from the base class and only has new constructors (that just delegate to the base class) and a new operator==. What I'd like to do is overload the operator Base&() in the Derived class so in cases where I need to interpret it as the Base. For example: class Base { Base(stuff); Base(const Base& that); bool operator==(Base& rhs); //typical equality test }; class Derived : public Base { Derived(stuff) : Base(stuff) {}; Derived(const Base& that) : Base(that) {}; Derived(const Derived& that) : Base(that) {}; bool operator==(Derived& rhs); //special case equality test operator Base&() { return (Base&)*this; //Is this OK? It seems wrong to me. } }; If you want a simple example of what I'm trying to do, pretend I had a String class and String==String is the typical character by character comparison. But I created a new class CaseInsensitiveString that did a case insensitive compare on CaseInsensitiveString==CaseInsensitiveString but in all other cases just behaved like a String. it doesn't even have any new data members, just an overloaded operator==. (Please, don't tell me to use std::string, this is just an example!) Am I going about this right? Something seems fishy, but I can't put my finger on it.

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• Is the following C code safe?

  - by lali

  #include<cstdio> #include<stdlib.h> int main() { char* ptr=NULL; printf("%s",ptr); return 0; } It prints (null) as output. The above is a sample code. In real code i get char* as a return of a function and i wish to print the character string for logging. However, NULL is also a valid return value of that function and so i am wondering if a null check is required before printing the character string? char* ptr=someFuncion(); // do i need the following if statement? if(ptr!=NULL) { printf("%s",ptr); } I just want to be sure that the output would be same i.e if ptr=NULL then output should be (null) on all platforms and compilers and the above code(without if statement) would not crash on any C standard compatible platform. In short, is the above code(without the if statement) standard compatible? Thanks for your help and patience :) Regards lali

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• Trouble with an depreciated constructor visual basic visual studio 2010

  - by VBPRIML

  My goal is to print labels with barcodes and a date stamp from an entry to a zebra TLP 2844 when the user clicks the ok button/hits enter. i found what i think might be the code for this from zebras site and have been integrating it into my program but part of it is depreciated and i cant quite figure out how to update it. below is what i have so far. The printer is attached via USB and the program will also store the entered numbers in a database but i have that part done. any help would be greatly Appreciated.   Public Class ScanForm      Inherits System.Windows.Forms.Form    Public Const GENERIC_WRITE = &H40000000    Public Const OPEN_EXISTING = 3    Public Const FILE_SHARE_WRITE = &H2      Dim LPTPORT As String    Dim hPort As Integer      Public Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String,                                                                           ByVal dwDesiredAccess As Integer,                                                                           ByVal dwShareMode As Integer, <MarshalAs(UnmanagedType.Struct)> ByRef lpSecurityAttributes As SECURITY_ATTRIBUTES,                                                                           ByVal dwCreationDisposition As Integer, ByVal dwFlagsAndAttributes As Integer,                                                                           ByVal hTemplateFile As Integer) As Integer          Public Declare Function CloseHandle Lib "kernel32" Alias "CloseHandle" (ByVal hObject As Integer) As Integer      Dim retval As Integer           <StructLayout(LayoutKind.Sequential)> Public Structure SECURITY_ATTRIBUTES          Private nLength As Integer        Private lpSecurityDescriptor As Integer        Private bInheritHandle As Integer      End Structure            Private Sub OKButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OKButton.Click          Dim TrNum        Dim TrDate        Dim SA As SECURITY_ATTRIBUTES        Dim outFile As FileStream, hPortP As IntPtr          LPTPORT = "USB001"        TrNum = Me.ScannedBarcodeText.Text()        TrDate = Now()          hPort = CreateFile(LPTPORT, GENERIC_WRITE, FILE_SHARE_WRITE, SA, OPEN_EXISTING, 0, 0)          hPortP = New IntPtr(hPort) 'convert Integer to IntPtr          outFile = New FileStream(hPortP, FileAccess.Write) 'Create FileStream using Handle        Dim fileWriter As New StreamWriter(outFile)          fileWriter.WriteLine(" ")        fileWriter.WriteLine("N")        fileWriter.Write("A50,50,0,4,1,1,N,")        fileWriter.Write(Chr(34))        fileWriter.Write(TrNum) 'prints the tracking number variable        fileWriter.Write(Chr(34))        fileWriter.Write(Chr(13))        fileWriter.Write(Chr(10))        fileWriter.Write("A50,100,0,4,1,1,N,")        fileWriter.Write(Chr(34))        fileWriter.Write(TrDate) 'prints the date variable        fileWriter.Write(Chr(34))        fileWriter.Write(Chr(13))        fileWriter.Write(Chr(10))        fileWriter.WriteLine("P1")        fileWriter.Flush()        fileWriter.Close()        outFile.Close()        retval = CloseHandle(hPort)          'Add entry to database        Using connection As New SqlClient.SqlConnection("Data Source=MNGD-LABS-APP02;Initial Catalog=ScannedDB;Integrated Security=True;Pooling=False;Encrypt=False"), _        cmd As New SqlClient.SqlCommand("INSERT INTO [ScannedDBTable] (TrackingNumber, Date) VALUES (@TrackingNumber, @Date)", connection)            cmd.Parameters.Add("@TrackingNumber", SqlDbType.VarChar, 50).Value = TrNum            cmd.Parameters.Add("@Date", SqlDbType.DateTime, 8).Value = TrDate            connection.Open()            cmd.ExecuteNonQuery()            connection.Close()        End Using          'Prepare data for next entry        ScannedBarcodeText.Clear()        Me.ScannedBarcodeText.Focus()      End Sub

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• Android - Read PNG image without alpha and decode as ARGB_8888

  - by loki666

  I try to read an image from sdcard (in emulator) and then create a Bitmap image with the BitmapFactory.decodeByteArray method. I set the options: options.inPrefferedConfig = Bitmap.Config.ARGB_8888 options.inDither = false Then I extract the pixels into a ByteBuffer. ByteBuffer buffer = ByteBuffer.allocateDirect(width*height*4) bitmap.copyPixelsToBuffer(buffer) I use this ByteBuffer then in the JNI to convert it into RGB format and want to calculate on it. But always I get false data - I test without modifying the ByteBuffer. Only thing I do is to put it into the native method into JNI. Then cast it into a unsigned char* and convert it back into a ByteBuffer before returning it back to Java. unsigned char* buffer = (unsinged char*)(env->GetDirectBufferAddress(byteBuffer)) jobject returnByteBuffer = env->NewDirectByteBuffer(buffer, length) Before displaying the image I get data back with bitmap.copyPixelsFromBuffer( buffer ) But then it has wrong data in it. My Question is if this is because the image is internally converted into RGB 565 or what is wrong here? ..... Have an answer for it: - yes, it is converted internally to RGB565. Does anybody know how to create such an bitmap image from PNG with ARGB8888 pixel format? If anybody has an idea, it would be great!

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• Pointers to structs

  - by Bobby

  I have the following struct: struct Datastore_T { Partition_Datastores_T cmtDatastores; // bytes 0 to 499 Partition_Datastores_T cdhDatastores; // bytes 500 to 999 Partition_Datastores_T gncDatastores; // bytes 1000 to 1499 Partition_Datastores_T inpDatastores; // bytes 1500 1999 Partition_Datastores_T outDatastores; // bytes 2000 to 2499 Partition_Datastores_T tmlDatastores; // bytes 2500 to 2999 Partition_Datastores_T sm_Datastores; // bytes 3000 to 3499 }; I want to set a char* to struct of this type like so: struct Datastore_T datastores; // Elided: datastores is initialized with data here char* DatastoreStartAddr = (char*)&datastores; memset(DatastoreStartAddr, 0, sizeof(Datastore_T)); The problem I have is that the value that DatastoreStartAddr points to always has a value of zero when it should point to the struct that has been initialized with data. Meaning if I change the values in the struct using the struct directly, the values pointed to by DatastoreStartAddr should also change b/c they are pointing to the same address. But this is not happening. What am I doing wrong?

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• Unit Testing Private Method in Resource Managing Class (C++)

  - by BillyONeal

  I previously asked this question under another name but deleted it because I didn't explain it very well. Let's say I have a class which manages a file. Let's say that this class treats the file as having a specific file format, and contains methods to perform operations on this file: class Foo { std::wstring fileName_; public: Foo(const std::wstring& fileName) : fileName_(fileName) { //Construct a Foo here. }; int getChecksum() { //Open the file and read some part of it //Long method to figure out what checksum it is. //Return the checksum. } }; Let's say I'd like to be able to unit test the part of this class that calculates the checksum. Unit testing the parts of the class that load in the file and such is impractical, because to test every part of the getChecksum() method I might need to construct 40 or 50 files! Now lets say I'd like to reuse the checksum method elsewhere in the class. I extract the method so that it now looks like this: class Foo { std::wstring fileName_; static int calculateChecksum(const std::vector<unsigned char> &fileBytes) { //Long method to figure out what checksum it is. } public: Foo(const std::wstring& fileName) : fileName_(fileName) { //Construct a Foo here. }; int getChecksum() { //Open the file and read some part of it return calculateChecksum( something ); } void modifyThisFileSomehow() { //Perform modification int newChecksum = calculateChecksum( something ); //Apply the newChecksum to the file } }; Now I'd like to unit test the calculateChecksum() method because it's easy to test and complicated, and I don't care about unit testing getChecksum() because it's simple and very difficult to test. But I can't test calculateChecksum() directly because it is private. Does anyone know of a solution to this problem?

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• fgets in c don't return a portion of an string

  - by Marc

  Hi! I'm totally new in C, and I'm trying to do a little application that searches a string into a file, my problem is that I need to open a big file (more than 1GB) with just one line inside and fgets return me the entire file (I'm doing test with a 10KB file). actually this is my code: #include <stdio.h> #include <string.h> int main(int argc, char *argv[]) { char *search = argv[argc-1]; int retro = strlen(search); int pun = 0; int sortida; int limit = 10; char ara[20]; FILE *fp; if ((fp = fopen ("SEARCHFILE", "r")) == NULL){ sortida = -1; exit (1); } while(!feof(fp)){ if (fgets(ara, 20, fp) == NULL){ break; } //this must be a 20 bytes line, but it gets the entyre 10Kb file printf("%s",ara); } sortida = 1; if(fclose(fp) != 0){ sortida = -2; exit (1); } return 0; } What can I do to find an string into a file? I'v tried with GREP but it don't helps, because it returns the position:ENTIRE_STRING. I'm open to ideas. Thanks in advance!

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• Error in VC++ for code that looks perfectly good C++?

  - by Ram Bhat

  Hey guys. Check out this piece of sample code. #include "stdafx.h" #include<conio.h> #include<string.h> class person{ private char name[20]; private int age; public void setValues(char n[],int a) { strcpy(this->name,n); this->age=a; } public void display() { printf("\nName = %s",name); printf("\nAge = %d",age); } }; int _tmain(int argc, _TCHAR* argv[]) { person p; p.setValues("ram",20); p.display(); getch(); return 0; } I am getting the following errors : 1------ Build started: Project: first, Configuration: Debug Win32 ------ 1 first.cpp 1c:\documents and settings\dark wraith\my documents\visual studio 2010\projects\first\first\first.cpp(9): error C2144: syntax error : 'char' should be preceded by ':' 1c:\documents and settings\dark wraith\my documents\visual studio 2010\projects\first\first\first.cpp(10): error C2144: syntax error : 'int' should be preceded by ':' 1c:\documents and settings\dark wraith\my documents\visual studio 2010\projects\first\first\first.cpp(12): error C2144: syntax error : 'void' should be preceded by ':' 1c:\documents and settings\dark wraith\my documents\visual studio 2010\projects\first\first\first.cpp(17): error C2144: syntax error : 'void' should be preceded by ':' ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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• C++ Check Substring of a String

  - by user69514

  I'm trying to check whether or not the second argument in my program is a substring of the first argument. The problem is that it only work if the substring starts with the same letter of the string. .i.e Michigan - Mich (this works) Michigan - Mi (this works) Michigan - igan (this doesn't work) #include <stdio.h> #include <string.h> #include <string> using namespace std; bool my_strstr( string str, string sub ) { bool flag = true; int startPosition = -1; char subStart = str.at(0); char strStart; //find starting position for(int i=0; i<str.length(); i++){ if(str.at(i) == subStart){ startPosition = i; break; } } for(int i=0; i<sub.size(); i++){ if(sub.at(i) != str.at(startPosition)){ flag = false; break; } startPosition++; } return flag; } int main(int argc, char **argv){ if (argc != 3) { printf ("Usage: check <string one> <string two>\n"); } string str1 = argv[1]; string str2 = argv[2]; bool result = my_strstr(str1, str2); if(result == 1){ printf("%s is a substring of %s\n", argv[2], argv[1]); } else{ printf("%s is not a substring of %s\n", argv[2], argv[1]); } return 0; }

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• When and why can sprintf fail?

  - by Srekel

  I'm using swprintf to build a string into a buffer (using a loop among other things). const int MaxStringLengthPerCharacter = 10 + 1; wchar_t* pTmp = pBuffer; for ( size_t i = 0; i < nNumPlayers ; ++i) { const int nPlayerId = GetPlayer(i); const int nWritten = swprintf(pTmp, MaxStringLengthPerCharacter, TEXT("%d,"), nPlayerId); assert(nWritten >= 0 ); pTmp += nWritten; } *pTaskPlayers = '\0'; If during testing the assert never hits, can I be sure that it will never hit in live code? That is, do I need to check if nWritten < 0 and handle that, or can I safely assume that there won't be a problem? Under which circumstances can it return -1? The documentation more or less just states "If the function fails". In one place I've read that it will fail if it can't match the arguments (i.e. the formatting string to the varargs) but that doesn't worry me. I'm also not worried about buffer overrun in this case - I know the buffer is big enough.

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• Accessing memory buffer after fread()

  - by xiongtx

  I'm confused as to how fread() is used. Below is an example from cplusplus.com /* fread example: read a complete file */ #include <stdio.h> #include <stdlib.h> int main () { FILE * pFile; long lSize; char * buffer; size_t result; pFile = fopen ( "myfile.bin" , "rb" ); if (pFile==NULL) {fputs ("File error",stderr); exit (1);} // obtain file size: fseek (pFile , 0 , SEEK_END); lSize = ftell (pFile); rewind (pFile); // allocate memory to contain the whole file: buffer = (char*) malloc (sizeof(char)*lSize); if (buffer == NULL) {fputs ("Memory error",stderr); exit (2);} // copy the file into the buffer: result = fread (buffer,1,lSize,pFile); if (result != lSize) {fputs ("Reading error",stderr); exit (3);} /* the whole file is now loaded in the memory buffer. */ // terminate fclose (pFile); free (buffer); return 0; } Let's say that I don't use fclose() just yet. Can I now just treat buffer as an array and access elements like buffer[i]? Or do I have to do something else?

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• C Programing - Return libcurl http response to string to the calling function

  - by empty set

  I have a homework and i need somehow to compare two http responses. I am writing it on C (dumb decision) and i use libcurl to make things easier. I am calling the function that uses libcurl to http request and response from another function and i want to return the http response to it. Anyway, the code below doesn't work, any ideas? #include <stdio.h> #include <curl/curl.h> #include <string.h> size_t write_data(void *ptr, size_t size, size_t nmemb, void *stream) { size_t written; written = fwrite(ptr, size, nmemb, stream); return written; } char *handle_url(void) { CURL *curl; char *fp; CURLcode res; char *url = "http://www.yahoo.com"; curl = curl_easy_init(); if (curl) { curl_easy_setopt(curl, CURLOPT_URL, url); curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data); curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp); res = curl_easy_perform(curl); if(res != CURLE_OK) fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res)); curl_easy_cleanup(curl); //printf("\n%s", fp); } return fp; } This solution C libcurl get output into a string works, but not in my case because i want to return this string to the calling function.

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• Unhandled Exception error message

  - by Joshua Green

  Does anyone know why including a term such as: t = PL_new_term_ref(); would cause an Unhandled Exception error message: 0xC0000005: Access violation reading location 0x0000000c. (Visual Studio 2008) I have a header file: class UserTaskProlog : public ArAction { public: UserTaskProlog( const char* name = " sth " ); ~UserTaskProlog( ); AREXPORT virtual ArActionDesired *fire( ArActionDesired currentDesired ); private: term_t t; }; and a cpp file: UserTaskProlog::UserTaskProlog( const char* name ) : ArAction( name, " sth " ) { char** argv; argv[ 0 ] = "libpl.dll"; PL_initialise( 1, argv ); PlCall( "consult( 'myProg.pl' )" ); } UserTaskProlog::~UserTaskProlog( ) { } ArActionDesired *UserTaskProlog::fire( ArActionDesired currentDesired ) { cout << " something " << endl; t = PL_new_term_ref( ); } Without t=PL_new_term_ref() everything works fine, but when I start adding my Prolog code (declarations first, such as t=PL_new_term_ref), I get this Access Violation error message. I'd appreciate any help. Thanks,

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• Arduino variable going blank after the first pass

  - by user541597

  I have an Arduino sketch that takes a timet and when that timet is equal to the current time it sets the new timet to timet + 2. For example: char* convert(char* x, String y) { int hour; int minute; sscanf(x, "%d:%d", &hour, &minute); char buf[6]; if (y == "6") { if (hour > 17) { hour = (hour+6)%24; snprintf(buf, 10, "%d:%d", hour, minute ); } else if (hour < 18) { //hour = hour + 6; minute = (minute + 2); snprintf(buf, 10, "%d:%d", hour, minute); } } if (y == "12") { if (hour > 11) { hour = (hour+12)%24; snprintf(buf, 10, "%d:%d", hour, minute ); } else if (hour < 12) { hour = hour + 12; snprintf(buf, 10, "%d:%d", hour, minute); } } if (y == "24") { hour = (hour+24)%24; snprintf(buf, 10, "%d:%d", hour, minute ); } return buf; } The sketch starts for example at 1:00am. timet is set to 1:02, at system time 1:02 timet is equal to the system time. My loops looks like this: if (timet == currenttime) { timet = convert(timet) } Whenever I check the value of timet it should equal 1:04, however I get the correct value at the first run after the execution of convert, however every time after that my timet value is blank. I tried changing the code instead of using the if loop. I only run the convert function when I send for example t through the serial monitor. This works fine and outputs the correct timet after the execution of the convert function, So I figured the problem is in the if loop... Any ideas?

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• How can I determine PerlLogHandler performance impact?

  - by Timmy

  I want to create a custom Apache2 log handler, and the template that is found on the apache site is: #file:MyApache2/LogPerUser.pm #--------------------------- package MyApache2::LogPerUser; use strict; use warnings; use Apache2::RequestRec (); use Apache2::Connection (); use Fcntl qw(:flock); use File::Spec::Functions qw(catfile); use Apache2::Const -compile => qw(OK DECLINED); sub handler { my $r = shift; my ($username) = $r->uri =~ m|^/~([^/]+)|; return Apache2::Const::DECLINED unless defined $username; my $entry = sprintf qq(%s [%s] "%s" %d %d\n), $r->connection->remote_ip, scalar(localtime), $r->uri, $r->status, $r->bytes_sent; my $log_path = catfile Apache2::ServerUtil::server_root, "logs", "$username.log"; open my $fh, ">>$log_path" or die "can't open $log_path: $!"; flock $fh, LOCK_EX; print $fh $entry; close $fh; return Apache2::Const::OK; } 1; What is the performance cost of the flocks? Is this logging process done in parallel, or in serial with the HTTP request? In parallel the performance would not matter as much, but I wouldn't want the user to wait another split second to add something like this.

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• How safe and reliable are C++ String Literals?

  - by DoctorT

  So, I'm wanting to get a better grasp on how string literals in C++ work. I'm mostly concerned with situations where you're assigning the address of a string literal to a pointer, and passing it around. For example: char* advice = "Don't stick your hands in the toaster."; Now lets say I just pass this string around by copying pointers for the duration of the program. Sure, it's probably not a good idea, but I'm curious what would actually be going on behind the scenes. For another example, let's say we make a function that returns a string literal: char* foo() { // function does does stuff return "Yikes!"; // somebody's feeble attempt at an error message } Now lets say this function is called very often, and the string literal is only used about half the time it's called: // situation #1: it's just randomly called without heed to the return value foo(); // situation #2: the returned string is kept and used for who knows how long char* retVal = foo(); In the first situation, what's actually happening? Is the string just created but not used, and never deallocated? In the second situation, is the string going to be maintained as long as the user finds need for it? What happens when it isn't needed anymore... will that memory be freed up then (assuming nothing points to that space anymore)? Don't get me wrong, I'm not planning on using string literals like this. I'm planning on using a container to keep my strings in check (probably std::string). I'm mostly just wanting to know if these situations could cause problems either for memory management or corrupted data.

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• Returning c_str from a function

  - by user199421

  This is from a small library that I found online: const char* GetHandStateBrief(const PostFlopState* state) { static std::ostringstream out; ... rest of the function ... return out.str().c_str() Now in my code I am doing this: const char *d = GetHandStateBrief(&post); std::cout<< d << std::endl; Now, at first d contained garbage. I then realized that the c string I am getting from the function is destroyed when the function returns because std::ostringstream is allocated on the stack. So I added: return strdup( out.str().c_str()); And now I can get the text I need from the function. I have two questions: 1) Am I understanding this correctly? 2) I later noticed that the ostringstream was was allocated with static storage. Doesn't that mean that the object is supposed to stay in memory until the program terminates? and if so , then why can't I access the string?

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• How to easily map c++ enums to strings

  - by Roddy

  I have a bunch of enum types in some library header files that I'm using, and I want to have a way of converting enum values to user strings - and vice-versa. RTTI won't do it for me, because the 'user strings' need to be a bit more readable than the enumerations. A brute force solution would be a bunch of functions like this, but I feel that's a bit too C-like. enum MyEnum {VAL1, VAL2,VAL3}; String getStringFromEnum(MyEnum e) { switch e { case VAL1: return "Value 1"; case VAL2: return "Value 2"; case VAL1: return "Value 3"; default: throw Exception("Bad MyEnum"); } } I have a gut feeling that there's an elegant solution using templates, but I can't quite get my head round it yet. UPDATE: Thanks for suggestions - I should have made clear that the enums are defined in a third-party library header, so I don't want to have to change the definition of them. My gut feeling now is to avoid templates and do something like this: char * MyGetValue(int v, char *tmp); // implementation is trivial #define ENUM_MAP(type, strings) char * getStringValue(const type &T) \ { \ return MyGetValue((int)T, strings); \ } ; enum eee {AA,BB,CC}; - exists in library header file ; enum fff {DD,GG,HH}; ENUM_MAP(eee,"AA|BB|CC") ENUM_MAP(fff,"DD|GG|HH") // To use... eee e; fff f; std::cout<< getStringValue(e); std::cout<< getStringValue(f);

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• Having some fun - what is a good way to include a secret key functionality and fire the KeyDown event?

  - by Sisyphus

  To keep myself interested, I try to put little Easter Eggs in my projects (mostly to amuse myself). I've seen some websites where you can type a series of letters "aswzaswz" and you get a "secret function" - how would I achieve this in C#? I've assigned a "secret function" in the past by using modifier keys bool showFunThing = (Control.ModifierKeys & Keys.Control) == Keys.Control; but wanted to get a bit more secretive (without the modifier keys) I just wanted the form to detect a certain word typed without any input ... I've built a method that I think should do it: private StringBuilder _pressedKeys = new StringBuilder(); protected override void OnKeyDown(KeyEventArgs e) { const string kWord = "fun"; char letter = (char)e.KeyValue; if (!char.IsLetterOrDigit(letter)) { return; } _pressedKeys.Append(letter); if (_pressedKeys.Length == kWord.Length) { if (_pressedKeys.ToString().ToLower() == kWord) { MessageBox.Show("Fun"); _pressedKeys.Clear(); } } base.OnKeyDown(e); } Now I need to wire it up but I can't figure out how I'm supposed to raise the event in the form designer ... I've tried this: this.KeyDown +=new System.Windows.Forms.KeyEventHandler(OnKeyDown); and a couple of variations on this but I'm missing something because it won't fire (or compile). It tells me that the OnKeyDown method is expecting a certain signature but I've got other methods like this where I haven't specified arguments. I fear that I may have got myself confused so I am turning to SO for help ... anyone?

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• Read whole ASCII file into C++ std::string

  - by Arrieta

  Hello, I need to read a whole file into memory and place it in a C++ std::string. If I were to read it into a char, the answer would be very simple: std::ifstream t; int lenght; t.open("file.txt", "r"); // open input file t.seekg(0, std::ios::end); // go to the end length = t.tellg(); // report location (this is the lenght) t.seekg(0, std::ios::beg); // go back to the beginning buffer = new char[length]; // allocate memory for a buffer of appropriate dimension t.read(buffer, length); // read the whole file into the buffer t.close(); // close file handle // ... do stuff with buffer here ... Now, I want to do the exact same thing, but using a std::string instead of a char. I want to avoid loops, i. e., I don't want to: std::ifstream t; t.open("file.txt", "r"); std::string buffer; std::string line; while(t){ std::getline(t, line); // ... append line to buffer and go on } t.close() any ideas?

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• Sending buffered images between Java client and Twisted Python socket server

  - by PattimusPrime

  I have a server-side function that draws an image with the Python Imaging Library. The Java client requests an image, which is returned via socket and converted to a BufferedImage. I prefix the data with the size of the image to be sent, followed by a CR. I then read this number of bytes from the socket input stream and attempt to use ImageIO to convert to a BufferedImage. In abbreviated code for the client: public String writeAndReadSocket(String request) { // Write text to the socket BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())); bufferedWriter.write(request); bufferedWriter.flush(); // Read text from the socket BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream())); // Read the prefixed size int size = Integer.parseInt(bufferedReader.readLine()); // Get that many bytes from the stream char[] buf = new char[size]; bufferedReader.read(buf, 0, size); return new String(buf); } public BufferedImage stringToBufferedImage(String imageBytes) { return ImageIO.read(new ByteArrayInputStream(s.getBytes())); } and the server: # Twisted server code here # The analog of the following method is called with the proper client # request and the result is written to the socket. def worker_thread(): img = draw_function() buf = StringIO.StringIO() img.save(buf, format="PNG") img_string = buf.getvalue() return "%i\r%s" % (sys.getsizeof(img_string), img_string) This works for sending and receiving Strings, but image conversion (usually) fails. I'm trying to understand why the images are not being read properly. My best guess is that the client is not reading the proper number of bytes, but I honestly don't know why that would be the case. Side notes: I realize that the char[]-to-String-to-bytes-to-BufferedImage Java logic is roundabout, but reading the bytestream directly produces the same errors. I have a version of this working where the client socket isn't persistent, ie. the request is processed and the connection is dropped. That version works fine, as I don't need to care about the image size, but I want to learn why the proposed approach doesn't work.

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• How to define and use a friend function to a temlate class with the same template?

  - by Narek

  I have written the following code: #include <iostream> using namespace std; template <class T> class AA { T a; public: AA() { a = 7; } friend void print(const AA<T> & z); }; template <class T> void print(const AA<T> & z) { cout<<"Print: "<<z.a<<endl; } void main() { AA<int> a; print<int>(a); } And getting the following error: error C2248: 'AA<T>::a' : cannot access private member declared in class 'AA<T>' 1> with 1> [ 1> T=int 1> ] 1> c:\users\narek\documents\visual studio 2008\projects\aaa\aaa\a.cpp(7) : see declaration of 'AA<T>::a' 1> with 1> [ 1> T=int 1> ] 1> c:\users\narek\documents\visual studio 2008\projects\aaa\aaa\a.cpp(30) : see reference to function template instantiation 'void print<int>(const AA<T> &)' being compiled 1> with 1> [ 1> T=int 1> ] What's wrong?

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