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• Which header files are necessary to run this code snippet?

  - by httpinterpret

  It's from here,but fails when compiling: int main(int argc, char **argv) { struct hostent { char *h_name; // main name char **h_aliases; // alternative names (aliases) int h_addrtype; // address type (usually AF_INET) int h_length; // length of address (in octets) char **h_addr_list; // alternate addresses (in Network Byte Order) }; #define h_addr h_addr_list[0] // First address of h_addr_list. struct hostent *info_stackoverflow; int i = 0; info_stackoverflow = gethostbyname( "www.stackoverflow.com" ); printf("The IP address of %s is %s", info_stackoverflow->h_name, inet_ntoa( * ((struct in_addr *)info_stackoverflow->h_addr ))); /* aliases */ while( *(pc_ip->h_aliases + i) != NULL ) { printf("\n\tAlias: %s", *(pc_ip->h_aliases + i) ); i++; } }

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• C Programming: malloc() inside another function

  - by vikramtheone

  Hi Guys, I need help with malloc() inside another function. I'm passing a pointer and size to the function from my main() and I would like to allocate memory for that pointer dynamically using malloc() from inside that called function, but what I see is that.... the memory which is getting allocated is for the pointer declared withing my called function and not for the pointer which is inside the main(). How should I pass a pointer to a function and allocate memory for the passed pointer from inside the called function? Can anyone throw light on this? Help!!! Vikram I have written the following code and I get the output as shown below SOURCE: main() { unsigned char *input_image; unsigned int bmp_image_size = 262144; if(alloc_pixels(input_image, bmp_image_size)==NULL) printf("\nPoint2: Memory allocated: %d bytes",_msize(input_image)); else printf("\nPoint3: Memory not allocated"); } signed char alloc_pixels(unsigned char *ptr, unsigned int size) { signed char status = NO_ERROR; ptr = NULL; ptr = (unsigned char*)malloc(size); if(ptr== NULL) { status = ERROR; free(ptr); printf("\nERROR: Memory allocation did not complete successfully!"); } printf("\nPoint1: Memory allocated: %d bytes",_msize(ptr)); return status; } PROGRAM OUTPUT: Point1: Memory allocated ptr: 262144 bytes Point2: Memory allocated input_image: 0 bytes

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• Interop Structure: Should Unsigned Short be Mapped to byte[]?

  - by Ngu Soon Hui

  I have such a C++ structure: typedef struct _FILE_OP_BLOCK { unsigned short fid; // objective file ID unsigned short offset; // operating offset unsigned char len; // buffer length(update) // read length(read) unsigned char buff[MAX_BUFF_SIZE]; } FILE_OP_BLOCK; And now I want to map it in .Net. The tricky thing is that the I should pass a 2 byte array for fid, and integer for len, even though in C# fid is an unsigned short and len is an unsigned char I wonder whether my structure ( in C#) below is correct? public struct File_OP_Block { [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)] public byte[] fid; public ushort offset; public byte length; [MarshalAs(UnmanagedType.ByValArray, SizeConst = 240)] public char[] buff; }

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• Unable to locate the Bug

  - by tzenes

  I was recently on The Daily WTF when I came across this old post. In it the author mentions that one of the programmers changed this code: int main (int argc, char **argv) { int x; char data_string[15]; ... x = 2; strcpy(data_string,"data data data"); ... } To this code: int main (int argc, char **argv) { int x = 2; char data_string[15] = "data data data"; ... } The author goes on to mention: [the coder] changed every single variable to be initiated on the stack For the life of me I cannot see how this change could be harmful, and I am worried that it is a lapse in my C knowledge. What is the WTF?

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• passing argument 1 of 'atoi' makes pointer from integer without a cast....can any body help me..

  - by somasekhar

  #include<stdio.h> #include<string.h> #include<stdlib.h> int main(){ int n; int a,b,ans[10000]; char *c,*d,*e; int i = 0; c = (char*)(malloc(20 * sizeof(char))); d = (char*)(malloc(20 * sizeof(char))); scanf("%d",&n); while(i < n){ scanf("%d",&a); scanf("%d",&b); itoa(a,c,10); itoa(b,d,10); a = atoi(strrev(c)) + atoi(strrev(d)); itoa(a,c,10); e = c; while(*e == '0')e++; ans[i] = atoi(strrev(e)); i++; } i = 0; while(i < n){ printf("%d\n",ans[i]); i++; } }

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• Potential problem with C standard malloc'ing chars.

  - by paxdiablo

  When answering a comment to another answer of mine here, I found what I think may be a hole in the C standard (c1x, I haven't checked the earlier ones and yes, I know it's incredibly unlikely that I alone among all the planet's inhabitants have found a bug in the standard). Information follows: Section 6.5.3.4 ("The sizeof operator") para 2 states "The sizeof operator yields the size (in bytes) of its operand". Para 3 of that section states: "When applied to an operand that has type char, unsigned char, or signed char, (or a qualified version thereof) the result is 1". Section 7.20.3.3 describes void *malloc(size_t sz) but all it says is "The malloc function allocates space for an object whose size is specified by size and whose value is indeterminate". It makes no mention at all what units are used for the argument. Annex E startes the 8 is the minimum value for CHAR_BIT so chars can be more than one byte in length. My question is simply this: In an environment where a char is 16 bits wide, will malloc(10 * sizeof(char)) allocate 10 chars (20 bytes) or 10 bytes? Point 1 above seems to indicate the former, point 2 indicates the latter. Anyone with more C-standard-fu than me have an answer for this?

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• using 'new' operator

  - by notLikeCpp

  I have simple task concerning 'new' operator. I need to create array of 10 chars and then input those chars using 'cin'. Should it look like this ? : char c = new char[10]; for(int i=0; i < 10; i++) { cin >> char[i] >> endl; }

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• quick java question

  - by j-unit-122

  private static char[] quicksort (char[] array , int left , int right) { if (left < right) { int p = partition(array , left, right); quicksort(array, left, p - 1 ); quicksort(array, p + 1 , right); } for (char i : array) System.out.print(i + ” ”); System.out.println(); return array; } private static int partition(char[] a, int left, int right) { char p = a[left]; int l = left + 1, r = right; while (l < r) { while (l < right && a[l] < p) l++; while (r > left && a[r] >= p) r--; if (l < r) { char temp = a[l]; a[l] = a[r]; a[r] = temp; } } a[left] = a[r]; a[r] = p; return r; } } hi guys just a quick question regarding the above coding, i know that the above coding returns the following B I G C O M P U T E R B C E G I M P U T O R B C E G I M P U T O R B C E G I M P U T O R B C E G I M P U T O R B C E G I M O P T U R B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U when the sequence BIGCOMPUTER is used but my question is can someone explain to me what is happening in the code and how? i know abit about the quick-sort algorithm but it doesnt seem to be the same in the above example.

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• Question about Virtual Inheritance hierarchy

  - by Summer_More_More_Tea

  Hi there: I encounter this problem when tackling with virtual inheritance. I remember that in a non-virtual inheritance hierarchy, object of sub-class hold an object of its direct super-class. What about virtual inheritance? In this situation, does object of sub-class hold an object of its super-class directly or just hold a pointer pointing to an object of its super-class? By the way, why the output of the following code is: sizeof(A): 8 sizeof(B): 20 sizeof(C): 20 sizeof(C): 36 Code: #include <iostream> using namespace std; class A{ char k[ 3 ]; public: virtual void a(){}; }; class B : public virtual A{ char j[ 3 ]; public: virtual void b(){}; }; class C : public virtual B{ char i[ 3 ]; public: virtual void c(){}; }; class D : public B, public C{ char h[ 3 ]; public: virtual void d(){}; }; int main( int argc, char *argv[] ){ cout << "sizeof(A): " << sizeof( A ) << endl; cout << "sizeof(B): " << sizeof( B ) << endl; cout << "sizeof(C): " << sizeof( C ) << endl; cout << "sizeof(D): " << sizeof( D ) << endl; return 0; } Thanks in advance. Kind regards.

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• C++ - what does the colon after a constructor mean?

  - by waitinforatrain

  I'd happily Google this but don't know what to call it to Google it. I have a piece of code here: class demo { private: unsigned char len, *dat; public: demo(unsigned char le = 5, unsigned char default) : len(le) { dat = new char[len]; for (int i = 0; i <= le; i++) dat[i] = default; } void ~demo(void) { delete [] *dat; } }; class newdemo : public demo { private: int *dat1; public: newdemo(void) : demo(0, 0) { *dat1 = 0; return 0; } }; (It's from a past exam paper and the question is to correct errors in the code so ignore errors!) My question is, what are the ": len(le) " and " : demo(0, 0)" called? Something to do with inheritance?

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• Problems with making a simple UNIX shell

  - by Kodemax

  Hai, I am trying to create a simple shell in UNIX. I read a lot and found that everybody uses the strtok a lot. But i want to do without any special functions. So i wrote the code but i cant seem to get it to work. Can anybody point out what i am doing wrong here? void process(char**); int arg_count; char **splitcommand(char* input) { char temp[81][81] ,*cmdptr[40]; int k,done=0,no=0,arg_count=0; for(int i=0 ; input[i] != '\0' ; i++) { k=0; while(1) { if(input[i] == ' ') { arg_count++; break; } if(input[i] == '\0') { arg_count++; done = 1; break; } temp[arg_count][k++] = input[i++]; } temp[arg_count][k++] = '\0'; if(done == 1) { break; } } for(int i=0 ; i<arg_count ; i++) { cmdptr[i] = temp[i]; cout<<endl; } cout<<endl; } void process(char* cmd[]) { int pid = fork(); if(pid < 0) { cout << "Fork Failed" << endl; exit(-1); } else if( pid == 0) { cout<<endl<<"in pid"; execvp(cmd[0], cmd); } else { wait(NULL); cout << "Job's Done" << endl; } } int main() { cout<<"Welcome to shell !!!!!!!!!!!"<<endl; char input[81]; cin.getline(input,81); splitcommand(input); }

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• what is the difference between 1 and 2 in follwing program?

  - by user323422

  template <class T> class ABC { public:void foo(T &a) { std::cout <<a; } void bar(T &b) { std::cout <<b; } }; template class ABC<char>; //#1 template void ABC<char>::foo(char &a); // #2

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• How to fill two-dimensional array using java enhanced loop?

  - by Shark

  Basically, I am trying this, but this only leaves array filled with zeros. I know how to fill it with normal for loop (such as for (int i = 0; i < array.length; i++) and so on), but why is my variant is not working? Any help would be appreciated. char[][] array = new char[x][y]; for (char[] row : array) for (char element : row) element = '~';

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• Can some tell me why I am seg faulting in this simple C program?

  - by user299648

  I keep on getting seg faulted after I end my first for loop, and for the life of me I don't why. The file I'm scanning is just 18 strings in 18 lines. I thinks the problem is the way I'm mallocing the double pointer called picks, but I don't know exactly why. I'm am only trying to scanf strings that are less than 15 chars long, so I don't see the problem. Can someone please help. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_LENGTH 100 int main( int argc,char *argv[] ) { char* string = malloc( 15*sizeof(char) ); char** picks = malloc(15*sizeof(char*)); FILE* pick_file = fopen( argv[l], "r" ); int num_picks; for( num_picks=0 ; fgets( string, MAX_LENGTH, pick_file ) != NULL ; num_picks++ ) { scanf( "%s", picks+num_picks ); } //this is where i seg fault int x; for(x=0; x<num_picks;x++) printf("s\n", picks+x); }

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• Struct Array Initialization and String Literals

  - by Christian Ammer

  Is following array initialization correct? I guess it is, but i'm not really sure if i can use const char* or if i better should use std::string. Beside the first question, do the char pointers point to memory segments of same sizes? struct qinfo { const char* name; int nr; }; qinfo queues[] = { {"QALARM", 1}, {"QTESTLONGNAME", 2}, {"QTEST2", 3}, {"QIEC", 4} };

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• Can someone tell me why I'm seg faulting in this simple C program?

  - by user299648

  I keep on getting seg faulted, and for the life of me I dont why. The file I'm scanning is just 18 strings in 18 lines. I thinks the problem is the way I'm mallocing the double pointer called picks, but I dont know exactly why. I'm am only trying to scanf strings that are less than 15 chars long, so I don't see the problem. Can someone please help. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_LENGTH 100 int main( int argc,char *argv[] ) { char* string = malloc( sizeof(char) ); char** picks = malloc(15*sizeof(char)); FILE* pick_file = fopen( argv[l], "r" ); int num_picks; for( num_picks=0 ; fgets( string, MAX_LENGTH, pick_file ) != NULL ; num_picks++ ) { printf("pick a/an %s ", string ); scanf( "%s", picks+num_picks ); } int x; for(x=0; x<num_picks;x++) printf("s\n", picks+x); }

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• python object to native c++ pointer

  - by Lodle

  Im toying around with the idea to use python as an embedded scripting language for a project im working on and have got most things working. However i cant seem to be able to convert a python extended object back into a native c++ pointer. So this is my class: class CGEGameModeBase { public: virtual void FunctionCall()=0; virtual const char* StringReturn()=0; }; class CGEPYGameMode : public CGEGameModeBase, public boost::python::wrapper<CGEPYGameMode> { public: virtual void FunctionCall() { if (override f = this->get_override("FunctionCall")) f(); } virtual const char* StringReturn() { if (override f = this->get_override("StringReturn")) return f(); return "FAILED TO CALL"; } }; Boost wrapping: BOOST_PYTHON_MODULE(GEGameMode) { class_<CGEGameModeBase, boost::noncopyable>("CGEGameModeBase", no_init); class_<CGEPYGameMode, bases<CGEGameModeBase> >("CGEPYGameMode", no_init) .def("FunctionCall", &CGEPYGameMode::FunctionCall) .def("StringReturn", &CGEPYGameMode::StringReturn); } and the python code: import GEGameMode def Ident(): return "Alpha" def NewGamePlay(): return "NewAlpha" def NewAlpha(): import GEGameMode import GEUtil class Alpha(GEGameMode.CGEPYGameMode): def __init__(self): print "Made new Alpha!" def FunctionCall(self): GEUtil.Msg("This is function test Alpha!") def StringReturn(self): return "This is return test Alpha!" return Alpha() Now i can call the first to functions fine by doing this: const char* ident = extract< const char* >( GetLocalDict()["Ident"]() ); const char* newgameplay = extract< const char* >( GetLocalDict()["NewGamePlay"]() ); printf("Loading Script: %s\n", ident); CGEPYGameMode* m_pGameMode = extract< CGEPYGameMode* >( GetLocalDict()[newgameplay]() ); However when i try and convert the Alpha class back to its base class (last line above) i get an boost error: TypeError: No registered converter was able to extract a C++ pointer to type class CGEPYGameMode from this Python object of type Alpha I have done alot of searching on the net but cant work out how to convert the Alpha object into its base class pointer. I could leave it as an object but rather have it as a pointer so some non python aware code can use it. Any ideas?

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• Argc/Argv C Problems

  - by Salman

  Hey all, If I have the following code: main(int argc, char *argv[]){ char serveradd[20]; strcpy(serveradd, argv[1]); int port = atoi(argv[2]); printf("%s %d \n", serveradd, port); The first two arguments to the command line are printed. However, if I do this: char serveradd[20]; strcpy(serveradd, argv[1]); int port = atoi(argv[2]); char versionnum[1]; strcpy(versionnum, argv[3]); printf("%s %d %s \n", serveradd, port, versionnum);` The first argument (serveradd) does not print out to the screen and is not being stored... Why is this happening and how can I fix it? Thanks!

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• What's the correct type to use for pointer subtraction on x64?

  - by Cheeso

  I'm just starting out with x64 compilation. I have a couple of char*'s, and I'm subtracting them. With a 32-bit compile, this works: char * p1 = .... char * p3 = ... int delta = p3 - p1; But if I compile for x64 I get a warning: warning C4244: 'initializing' : conversion from '__int64' to 'int', possible loss of data What is the correct type to use, to represent a difference between two pointers, that works in both x86 and x64 compiles?

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• How do the operators < and > work with pointers?

  - by Øystein

  Just for fun, I had a std::list of const char*, each element pointing to a null-terminated text string, and ran a std::list::sort() on it. As it happens, it sort of (no pun intended) did not sort the strings. Considering that it was working on pointers, that makes sense. According to the documentation of std::list::sort(), it (by default) uses the operator < between the elements to compare. Forgetting about the list for a moment, my actual question is: How do these (, <, =, <=) operators work on pointers in C++ and C? Do they simply compare the actual memory addresses? char* p1 = (char*) 0xDAB0BC47; char* p2 = (char*) 0xBABEC475; e.g. on a 32-bit, little-endian system, p1 p2 because 0xDAB0BC47 0xBABEC475? Testing seems to confirm this, but I thought it'd be good to put it on StackOverflow for future reference. C and C++ both do some weird things to pointers, so you never really know...

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• oracle collection not enough values

  - by john

  I did following: create or replace type my_row as object ( lname varchar2(30), fname varchar2(30), MI char(1), hohSSN char (9), hohname VARCHAR2(63), hohDob char(10), dob DATE ); create or replace type eiv.my_rec as table of eiv.my_row; but then doing query like: my_records my_rec select '', '', '', '', '', '', sysdate bulk collect into my_records from dual; gives error ORA-00947: not enough values what can i be doing wrong here?

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• Make: how make all hidden files in the current makefile?

  - by HH

  It traverses to bottom dirs for some unknown reason: Errorsome /bin/sh: .??*: not found make[23]: Entering directory `/m/user/files/dir' make clean Makefile all: make clean #The wildcard is the bug. I want to make all hidden files in the current makefile. #It should match .<some char><some char><any char arbitrary times> make $$(.??*) #I want to replace below-like-tihngs with a wildcard above # make .lambda # make .lambda_t clean: -rm .??* .lambda: #do something .lambda_t:

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• How do we simplify this kind of code in Java? Something like macros in C?

  - by Terry Li

  public static boolean diagonals(char[][] b, int row, int col, int l) { int counter = 1; // because we start from the current position char charAtPosition = b[row][col]; int numRows = b.length; int numCols = b[0].length; int topleft = 0; int topright = 0; int bottomleft = 0; int bottomright = 0; for (int i=row-1,j=col-1;i>=0 && j>=0;i--,j--) { if (b[i][j]==charAtPosition) { topleft++; } else { break; } } for (int i=row-1,j=col+1;i>=0 && j<=numCols;i--,j++) { if (b[i][j]==charAtPosition) { topright++; } else { break; } } for (int i=row+1,j=col-1;i<=numRows && j>=0;i++,j--) { if (b[i][j]==charAtPosition) { bottomleft++; } else { break; } } for (int i=row+1,j=col+1;i<=numRows && j<=numCols;i++,j++) { if (b[i][j]==charAtPosition) { bottomright++; } else { break; } } return topleft + bottomright + 1 >= l || topright + bottomleft + 1 >= l; //in this case l is 5 } After I was done posting the code above here, I couldn't help but wanted to simplify the code by merging the four pretty much the same loops into one method. Here's the kind of method I want to have: public int countSteps(char horizontal, char vertical) { } Two parameters horizontal and vertical can be either + or - to indicate the four directions to walk in. What I want to see if possible at all is i++; is generalized to i horizontal horizontal; when horizontal taking the value of +. What I don't want to see is if or switch statements, for example: public int countSteps(char horizontal, char vertical) { if (horizontal == '+' && vertical == '-') { for (int i=row-1,j=col+1;i>=0 && j<=numCols;i--,j++) { if (b[i][j]==charAtPosition) { topright++; } else { break; } } } else if (horizontal == '+' && vertical == '+') { for (int i=row+1,j=col+1;i>=0 && j<=numCols;i++,j++) { if (b[i][j]==charAtPosition) { topright++; } else { break; } } } else if () { } else { } } Since it is as tedious as the original one. Note also that the comparing signs for the loop condition i>=0 && j<=numCols; for example, >= && <= have correspondence with the value combination of horizontal and vertical. Sorry for my bad wording, please let me know if anything is not clear.

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• Why is my implementation of strcmp not returning the proper value?

  - by Avanish Giri

  Why is this printing out 0 back in main but 6 when it is inside of the strcmp function? 7 int main() 8 { 9 char* str = "test string"; 10 char* str2 = "test strong"; 11 //printf("string length = %d\n",strlen(str)); 12 13 int num = strcmp(str,str2); 14 15 printf("num = %d\n",num); 16 } 29 int strcmp(char* str, char* str2) 30 { 31 if(*str == '\0' && *str2 == '\0') 32 return 0; 33 if(*str2 - *str == 0) 34 { 35 strcmp(str+1,str2+1); 36 } 37 else 38 { 39 int num = *str2 - *str; 40 cout << "num = " <<num<<endl; 41 return num; 42 } 43 } The output is: num = 6 num = 0 Why is it printing 0 when obviously the value that it should be returning is 6?

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• Reading data from text file in C

  - by themake

  I have a text file which contains words separated by space. I want to take each word from the file and store it. So i have opened the file but am unsure how to assign the word to a char. FILE *fp; fp = fopen("file.txt", "r"); //then i want char one = the first word in the file char two = the second word in the file

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