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• Is it good practice to initialize array in C/C++?

  - by sand

  I recently encountered a case where I need to compare two files (golden and expected) for verification of test results and even though the data written to both the files were same, the files does not match. On further investigation, I found that there is a structure which contains some integers and a char array of 64 bytes, and not all the bytes of char array were getting used in most of the cases and unused fields from the array contain random data and that was causing the mismatch. This brought me ask the question whether it is good practice to initialize the array in C/C++ as well, as it is done in Java?

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• parsing command option with default values and range constrains in C

  - by agramfort

  Hi, I need to parse command line arguments in C. My arguments are basically int or float with default values and range constrains. I've started to implement something that look like this: option_float(float* out, int argc, char* argv, char* name, description, float default_val, int is_optional, float min_value, float max_value) which I call for example with: float* pct; option_float(pct, argc, argv, "pct", "My super percentage option", 50, 1, FALSE, 0, 100) however I don't want to reinvent the wheel ! My objective is to have error checking of range constrains, throw an error when the option is not optional and is not set. And generate the help message usually given by usage() function. The usage text would look like this: --pct My super percentage option (default : 50). Should be in [0, 100] I've started with getopt but it is too limited for what I want to do and I feel it still requires me to write too much code for a simple usecase like this. thanks

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• strenge exception phenomenon in win7

  - by Level 2

  Hello all, I spot some interesting artcles about exception handle in codeproject http://www.codeproject.com/KB/cpp/seexception.aspx after reading, I decided to do some experiment. The first time I try to excute the following code char *p; p[0] = 0; The program died without question. But After serveral time I execute the same problem binary code. It magically did fine. even the following code is doing well. any clue or explain? char *p p[1000] = 'd'; cout<<p[1000]<<endl; my os is windows 7 64bit and compiler is vs2008 rc1.

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• How can I remove the head of a main function?

  - by Nathan McDavitt-Van Fleet

  I am trying to move some code from a seperate binary and have it inside my main program. Unfortunately I can't mimic the initialization variables for the main function. How can I create argc and argv by hand? Can someone give me some example assignments. since it looks like this: int main(int argc, char *argv[]) I figured I could assign them like this: int argc=1; char *argv[0]="Example"; But it doesn't work. Can anyone tell me how this might be done?

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• How can I obtain the IPv4 address of the client?

  - by Dr Dork

  Hello! I'm prepping for a simple work project and am trying to familiarize myself with the basics of socket programming in a Unix dev environment. At this point, I have some basic server side code setup to listen for incoming TCP connection requests from clients after the parent socket has been created and is set to listen... int sockfd, newfd; unsigned int len; socklen_t sin_size; char msg[]="Test message sent"; char buf[MAXLEN]; int st, rv; struct addrinfo hints, *serverinfo, *p; struct sockaddr_storage client; char ip[INET6_ADDRSTRLEN]; . . //parent socket creation and listen code omitted for simplicity . //wait for connection requests from clients while(1) { //Returns the socketID and address of client connecting to socket if( ( newfd = accept(sockfd, (struct sockaddr *)&client, &len) ) == -1 ){ perror("Accept"); exit(-1); } if( (rv = recv(newfd, buf, MAXLEN-1, 0 )) == -1) { perror("Recv"); exit(-1); } struct sockaddr_in *clientAddr = ( struct sockaddr_in *) get_in_addr((struct sockaddr *)&client); inet_ntop(client.ss_family, clientAddr, ip, sizeof ip); printf("Receive from %s: query type is %s\n", ip, buf); if( ( st = send(newfd, msg, strlen(msg), 0)) == -1 ) { perror("Send"); exit(-1); } //ntohs is used to avoid big-endian and little endian compatibility issues printf("Send %d byte to port %d\n", ntohs(clientAddr->sin_port) ); close(newfd); } } I found the get_in_addr function online and placed it at the top of my code and use it to obtain the IP address of the client connecting... // get sockaddr, IPv4 or IPv6: void *get_in_addr(struct sockaddr *sa) { if (sa->sa_family == AF_INET) { return &(((struct sockaddr_in*)sa)->sin_addr); } return &(((struct sockaddr_in6*)sa)->sin6_addr); } but the function always returns the IPv6 IP address since thats what the sa_family property is set as. My question is, is the IPv4 IP address stored anywhere in the data I'm using and, if so, how can I access it? Thanks so much in advance for all your help!

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• delete & new in c++

  - by singh

  Hi This may be very simple question,But please help me. i wanted to know what exactly happens when i call new & delete , For example in below code char * ptr=new char [10]; delete [] ptr; call to new returns me memory address. Does it allocate exact 10 bytes on heap, Where information about size is stored.When i call delete on same pointer,i see in debugger that there are a lot of byte get changed before and after the 10 Bytes. Is there any header for each new which contain information about number of byte allocated by new. Thanks a lot

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• new operator overwriting an existing object

  - by dvpdiner2

  I have a custom FastStack class, implemented as a fixed size array and an index into that array. In my copy constructor, I allocate the array and then assign each object from the copy's array into the new array. There's some refcounting in the objects on the stack, hence assignment is used rather than a simple copy. The problem is that when allocating the array, it sometimes overwrites part of the other stack's array. As can be expected, this leads to eventual segmentation faults when that data is dereferenced. class FastStack { private: int m_size, m_ptr; ObjectRef* m_stack; public: FastStack(int size) : m_size(size), m_ptr(-1) { m_stack = new ObjectRef[m_size]; } FastStack(const FastStack& copy) : m_size(copy.m_size), m_ptr(copy.m_ptr) { long a = (long)copy.m_stack[0]; m_stack = new ObjectRef[m_size]; if ((long)copy.m_stack[0] != a) fprintf(stderr, "\nWe have a serious problem!\n\n"); for (int i = 0; i <= m_ptr; i++) m_stack[i] = copy.m_stack[i]; } ~FastStack() { delete[] m_stack; } }; class ObjectRef { private: DataObj* m_obj; public: ObjectRef() : m_obj(0) { } ObjectRef(DataObj* obj) : m_obj(obj) { if (m_obj) m_obj->addRef(); } ObjectRef(const ObjectRef& obj) : m_obj(obj.m_obj) { if (m_obj) m_obj->addRef(); } ~ObjectRef() { if (m_obj) m_obj->delRef(); } ObjectRef& operator=(DataObj* obj) { if (obj) obj->addRef(); if (m_obj) m_obj->delRef(); m_obj = obj; return *this; } ObjectRef& operator=(const ObjectRef& obj) { if (obj.m_obj) obj.m_obj->addRef(); if (m_obj) m_obj->delRef(); m_obj = obj.m_obj; return *this; } }; I see that "We have a serious problem!" line shortly before a segfault, and stepping through it with gdb I can see that one of the ObjectRefs created by new has the same address as the other stack's array. My first instinct is to say that new should never be allocating memory that is already in use, but that clearly seems to be the case here and I am at a complete loss as to what can be done. Added: At the time that I see this happen, m_size = 2 and m_ptr = 0.

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• Evaluation of (de)reference operators

  - by Micha

  I have an (uncommented...) source file which I'm trying to understand. static const Map *gCurMap; static std::vector<Map> mapVec; then auto e = mapVec.end(); auto i = mapVec.begin(); while(i!=e) { // ... const Map *map = gCurMap = &(*(i++)); // ... } I don't understand what &(*(i++)) does. It does not compile when just using i++, but to me it looks the same, because I'm "incrementing" i, then I'm requesting the value at the given address and then I'm requesting the address of this value?!

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• c: memory allocation (what's going on)

  - by facha

  Hi, everyone Please take a look at this piece of code. I'm allocating one byte for the first variable and another byte for the second one. However, it seems like the compiler allocates more (or I'm missing something). The program outputs both strings, even though their length is more the one byte. void main() { char* some1 = malloc(1); sprintf(some1,"cool"); char* some2 = malloc(1); sprintf(some2,"face"); printf("%s ",some1); printf("%s\n",some2); } Please, could anyone spot some light on what's going on when memory is being allocated.

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• Why isn't the copy constructor elided here?

  - by Jesse Beder

  (I'm using gcc with -O2.) This seems like a straightforward opportunity to elide the copy constructor, since there are no side-effects to accessing the value of a field in a bar's copy of a foo; but the copy constructor is called, since I get the output meep meep!. #include <iostream> struct foo { foo(): a(5) { } foo(const foo& f): a(f.a) { std::cout << "meep meep!\n"; } int a; }; struct bar { foo F() const { return f; } foo f; }; int main() { bar b; int a = b.F().a; return 0; }

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• How to check whether iterators form a contiguous memory zone?

  - by Vincent

  I currently have the following function to read an array or a vector of raw data (_readStream is a std::ifstream) : template<typename IteratorType> inline bool MyClass::readRawData( const IteratorType& first, const IteratorType& last, typename std::iterator_traits<IteratorType>::iterator_category* = nullptr ) { _readStream.read(reinterpret_cast<char*>(&*first), (last-first)*sizeof(*first)); return _readStream.good(); } First question : does this function seem ok for you ? As we read directly a block of memory, it will only work if the memory block from first to last is contiguous in memory. How to check that ?

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• how to send Zip(binary) file Through HTTP post method in mFC/C++?

  - by Mahantesh

  I am posting the file to server and its working fine, But the my code fails when i try to post the .zip file. May be my code is wrong in the reading the zip file contents data. ifstream::pos_type size; char * memblock; ifstream file ("example.zip", ios::in|ios::binary|ios::ate); if (file.is_open()) { size = file.tellg(); memblock = new char [size]; file.seekg (0, ios::beg); file.read (memblock, size); file.close(); postBody.AppendFormat("Content-Disposition: form-data; name=\"datafile\"; filename=\"%s\"; \r\n\n%s", zipFilePath, memblock); postBody.AppendFormat("\r\n--%s--\r\n", boundary); }

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• Using pipes inside a class in C++

  - by Paul

  I'm trying to use this tutorial to make plots with Gnuplot in C++. However I will be using the pipe to Gnuplot from within a class, but then I run into some problems: I've got a header file where I declare all variables etc. I need to declare the pipe-variable here too, but how do I do that? I've tried doing it straight away, but it doesn't work: Logger.h: class Logger { FILE pipe; } Logger.cpp: Logger::Logger() { //Constructor *pipe = popen("gnuplot -persist","w"); } Gives the error Logger.cpp:28: error: no match for ‘operator=’ in ‘*((Logger*)this)->Logger::pipe = popen(((const char*)"gnuplot -persist"), ((const char*)"w"))’ Suggestions?

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• Storing objects in STL vector - minimal set of methods

  - by osgx

  Hello What is "minimal framework" (necessary methods) of object, which I will store in STL <vector>? For my assumptions: #include <vector> #include <cstring> using namespace std; class Doit { private: char *a; public: Doit(){a=(char*)malloc(10);} ~Doit(){free(a);} }; int main(){ vector<Doit> v(10); } gives *** glibc detected *** ./a.out: double free or corruption (fasttop): 0x0804b008 *** Aborted and in valgrind: malloc/free: 2 allocs, 12 frees, 50 bytes allocated.

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• How to call operator<< on "this" in a descendant of std::stringstream?

  - by romkyns

  class mystream : public std::stringstream { public: void write_something() { this << "something"; } }; This results in the following two compile errors on VC++10: error C2297: '<<' : illegal, right operand has type 'const char [10]' error C2296: '<<' : illegal, left operand has type 'mystream *const ' Judging from the second one, this is because what this points at can't be changed, but the << operator does (or at least is declared as if it does). Correct? Is there some other way I can still use the << and >> operators on this?

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• Can you use #defined values in if statements (In C programs)?

  - by Jordan S

  I am new at C programming. I thought when you type something like #define Const 5000 that the compiler just replaces every instance of Const with 5000 at compile time. Is that wrong? I try doing this in my code and I get a syntax error. Why can't i do this? #define STEPS_PER_REV 12345 ... in some function if(CurrentPosition >= STEPS_PER_REV) { // do some stuff here } The compiler complains about the if statement with a syntax error that gives me no details.

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• quick sort problem

  - by farka

  I use qsort from C libary and I have datatype Element_type **pElement and Element_type is struct typedef element_type {int ,char ....} example, and i call quicksor function with qsort(*pElement,iCountElement,(size_t)sizeof(Element_type),compare); and callback function static int compare(const void *p1, const void *p2) { Element_type *a1 = (Element_type *)p1; Element_type *a2 = (Element_type *)p2; return ( (a2)->iServiceId < (a1)->iServiceId ); } but I always get segmentation fault. Why?

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• Question about C Pointers (just learning)

  - by Mike

  I am curious as to why this is an error and what the error message means. Here is some code. int *x[] = {"foo", "bar", "baz"}; int *y[] = {"foo", "bar", "baz"}; x = y; I try to compile and I get this: error: incompatible types when assigning to type ‘char [3]’ from type ‘char *’ Question #1 why is this an error? and Question #2 why are the types different? Thanks for you help.

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• Correct way to initialize a NULL-terminated array of strings in C

  - by jjardon

  Is this code correct? char *argv[] = { "foo", "bar", NULL };

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• Is there any memory leak in the normal routine of sqlite3_*()?

  - by reer

  A normal routine of sqlite3_prepare_v2() + sqlite3_step() + sqlite3_finalize() could contain leak. It sound ridiculous. But the test code seems to say it. Or I used the sqlite3_*() wrongly. Appreciate for any reply. __code________________________ include include // for usleep() include int multi_write (int j); sqlite3 *db = NULL; int main (void) { int ret = -1; ret = sqlite3_open("test.db", &db); ret = sqlite3_exec(db,"CREATE TABLE data_his (id INTEGER PRIMARY KEY, d1 CHAR(16))", NULL,NULL,NULL); usleep (100000); int j=0; while (1) { multi_write (j++); usleep (2000000); printf (" ----------- %d\n", j); } ret = sqlite3_close (db); return 0; } int multi_write (int j) { int ret = -1; char *sql_f = "INSERT OR REPLACE INTO data_his VALUES (%d, %Q)"; char *sql = NULL; sqlite3_stmt *p_stmt = NULL; ret = sqlite3_prepare_v2 (db, "BEGIN TRANSACTION", -1, &p_stmt, NULL); ret = sqlite3_step ( p_stmt ); ret = sqlite3_finalize ( p_stmt ); int i=0; for (i=0; i<100; i++) { sql = sqlite3_mprintf ( sql_f, j*100000 + i, "00000000000068FD"); ret = sqlite3_prepare_v2 (db, sql, -1, &p_stmt, NULL ); sqlite3_free ( sql ); //printf ("sqlite3_prepare_v2(): %d, %s\n", ret, sqlite3_errmsg (db)); ret = sqlite3_step ( p_stmt ); //printf ("sqlite3_step(): %d, %s\n", ret, sqlite3_errmsg (db)); ret = sqlite3_finalize ( p_stmt ); //printf ("sqlite3_finalize(): %d, %s\n\n", ret, sqlite3_errmsg (db)); } ret = sqlite3_prepare_v2 (db, "COMMIT TRANSACTION", -1, &p_stmt, NULL ); ret = sqlite3_step ( p_stmt ); ret = sqlite3_finalize ( p_stmt ); return 0; } __result________________________ And I watch the the process's run by top. At first, the memory statistics is: PID PPID USER STAT VSZ %MEM %CPU COMMAND 17731 15488 root S 1104 5% 7% ./sqlite3multiwrite When the printf() in while(1){} of main() prints the 150, the memory statistics is: PID PPID USER STAT VSZ %MEM %CPU COMMAND 17731 15488 root S 1552 5% 7% ./sqlite3multiwrite It sounds that after 150 for-cycles, the memory used by sqlite3multiwrite increase from 1104KB to 1552KB. What does it mean? memory leak or other thing?

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• Encryption By Certificate

  - by user1817240

  I am encrypting customer name in database at database level. While saving in database only first letter of customer name is saved and hence while decrypting only first letter is retrieved. The following code shows the test sp. ALTER PROCEDURE [dbo].[spc_test_insert] ( @sFIRST_NAME typ_encryptedtext, ) AS BEGIN DECLARE @sSENCRYPTION_KEY char(15) DECLARE @sCERTIFICATE char(22) SET @sSENCRYPTION_KEY='SymmetricKey1' SET @sCERTIFICATE='CustomerCertificate' OPEN SYMMETRIC KEY SymmetricKey1 DECRYPTION BY CERTIFICATE CustomerCertificate; INSERT INTO test_table ( FIRST_NAME, ) Values ( -- Add the Params to be Added... EncryptByKey(Key_GUID(@sSENCRYPTION_KEY),@sFIRST_NAME), ) CLOSE SYMMETRIC KEY SymmetricKey1 END encryption decryption working fine in normal insert but its not working in stored procedure.

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• an error "variable of field declared void"

  - by lego69

  I have this code: header - test.h Inside header I have some class Z and definitions of two functions test and test2 I call function test2 from test void test2(Z z, Z const *za); this is implementation of the function: void test2(Z z, Z const *za){ int i = z; //this row works cout << i << endl; } I call it from test: test2(z1, za1); // za1 is pinter to object and z1 is some object but in my header I receive an 3 errors: Multiple markers at this line - initializer expression list treated as compound expression - `A' was not declared in this scope - variable or field `quiz2' declared void can somebody please explain why? thanks in advance

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• Create a modifiable string literal in C++

  - by Anne

  Is it possible to create a modifiable string literal in C++? For example: char* foo[] = { "foo", "foo" }; char* afoo = foo[0]; afoo[2] = 'g'; // access violation This produces an access violation because the "foo"s are allocated in read only memory (.rdata section I believe). Is there any way to force the "foo"s into writable memory (.data section)? Even via a pragma would be acceptable! (Visual Studio compiler) I know I can do strdup and a number of other things to get around the problem, but I want to know specifically if I can do as I have asked. :)

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• strftimedoesnt display year correctly

  - by paultop6

  Hi guys, i have the following code below: const char* timeformat = "%Y-%m-%d %H:%M:%S"; const int timelength = 20; char timecstring[timelength]; strftime(timecstring, timelength, timeformat, currentstruct); cout << "timecstring is: " << timecstring << "\n"; currentstruct is a tm*. The cout is giving me the date in the correct format, but the year is not 2010, but 3910. I know there is something to do with the year cound starting at 1900, but im not sure how to get strftime to recognise this and not add 1900 to the value of 2010 that is there, can anyone help. Regards Paul

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• hash table with chaining method program freezing

  - by Justin Carrey

  I am implementing hash table in C using linked list chaining method. The program compiles but when inserting a string in hash table, the program freezes and gets stuck. The program is below: struct llist{ char *s; struct llist *next; }; struct llist *a[100]; void hinsert(char *str){ int strint, hashinp; strint = 0; hashinp = 0; while(*str){ strint = strint+(*str); } hashinp = (strint%100); if(a[hashinp] == NULL){ struct llist *node; node = (struct llist *)malloc(sizeof(struct llist)); node->s = str; node->next = NULL; a[hashinp] = node; } else{ struct llist *node, *ptr; node = (struct llist *)malloc(sizeof(struct llist)); node->s = str; node->next = NULL; ptr = a[hashinp]; while(ptr->next != NULL){ ptr = ptr->next; } ptr->next = node; } } void hsearch(char *strsrch){ int strint1, hashinp1; strint1 = 0; hashinp1 = 0; while(*strsrch){ strint1 = strint1+(*strsrch); } hashinp1 = (strint1%100); struct llist *ptr1; ptr1 = a[hashinp1]; while(ptr1 != NULL){ if(ptr1->s == strsrch){ cout << "Element Found\n"; break; } else{ ptr1 = ptr1->next; } } if(ptr1 == NULL){ cout << "Element Not Found\n"; } } hinsert() is to insert elements into hash and hsearch is to search an element in the hash. Hash function is written inside hinsert() itself. In the main(), what i am initializing all the elements in a[] to be NULL like this: for(int i = 0;i < 100; i++){ a[i] = NULL; } Help is very much appreciated. Thanks !

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