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  • Why does this program segfault

    - by Leda
    Upon compiling and running this small program to reverse a string, I get a Segmentation Fault before any output occurs. Forgive me if this is an obvious question, I'm still very new to C. #include <stdio.h> int reverse(char string[], int length); int main() { char string[] = "reversed"; printf("String at start of main = %s", string); reverse(string, sizeof(string)); printf("%s\n", string); return 0; } // Reverse string int reverse(char string[], int length) { int i; char reversed[] = {}; int temp; for(i = 0; i < length; ++i) { temp = string[i]; reversed[length - i] = temp; } return 0; }

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  • How can I find out how much memory an object of a C++ class consumes?

    - by Shadow
    Hi, I am developing a Graph-class, based on boost-graph-library. A Graph-object contains a boost-graph, so to say an adjacency_list, and a map. When monitoring the total memory usage of my program, it consumes quite a lot (checked with pmap). Now, I would like to know, how much of the memory is exactly consumed by a filled object of this Graph-class? With filled I mean when the adjacency_list is full of vertices and edges. I found out, that using sizeof() doesn't bring me far. Using valgrind is also not an alternative as there is quite some memory allocation done previously and this makes the usage of valgrind impractical for this purpose. I'm also not interested in what other parts of the program cost in memory, I want to focus on one single object. Thank you.

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  • Increase a recive buffer in UDP socket

    - by unresolved_external
    I'wm writing an app, which transmits video and obviously uses UDP protocol fot this purpose. So I am wondering how can I increase a size of send/recieve buffer, cause currently the maximal size of data, which I can send is 65000 bytes. I already tried to do it in following way: int option = 262144; if(setsockopt(m_SocketHandle,SOL_SOCKET,SO_RCVBUF ,(char*)&option,sizeof(option)) < 0) { printf("setsockopt failed\n"); } But it did not work. So how can I do it?

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  • Allocate from buffer in C

    - by Grimless
    I am building a simple particle system and want to use a single array buffer of structs to manage my particles. That said, I can't find a C function that allows me to malloc() and free() from an arbitrary buffer. Here is some pseudocode to show my intent: Particle* particles = (Particle*) malloc( sizeof(Particle) * numParticles ); Particle* firstParticle = <buffer_alloc>( particles ); initialize_particle( firstParticle ); // ... Some more stuff if (firstParticle->life < 0) <buffer_free>( firstParticle ); // @ program's end free(particles); Where <buffer_alloc> and <buffer_free> are functions that allocate and free memory chunks from arbitrary pointers (possibly with additional metadata such as buffer length, etc.). Do such functions exist and/or is there a better way to do this? Thank you!

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  • Is it bad practice to declare an array mid-function...

    - by Maximus
    In C, which would be more proper... void MyFunction() { int* array; int size; //do a bunch of stuff size = 10; array = (int*)(sizeof(int)*size); //do more stuff... //no longer need array... free(array); } Or is something like this okay? void MyFunction() { int size; //do a bunch of stuff size = 10; array[size]; //do more stuff... } The malloc uses the heap instead of the stack, so I suppose if you know size is going to be very large you'd want to malloc... but if you're quite certain size will be small enough, would the second method be reasonable?

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  • Operators vs Functions in C/C++

    - by user356106
    Someone recently asked me the difference between a C++ standard operator (e.g. new,delete,sizeof) and function (e.g. tan,delete, malloc). By "standard" I mean those provided by default by the compiler suite, and not user defined. Below were the answers I gave, though neither seemed satisfactory. (1) An operator doesn't need any headers to be included to use it : E.g. you can have a call to new without including any headers. However, a function (say free() ) does need headers included, compulsorily. (2) An operator is defined as such (ie as a class operator) somewhere in the standard headers. A function isn't. Can you critique these answers and give me a better idea of the difference?

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  • zeroing out memory

    - by robUK
    Hello, gcc 4.4.4 c89 I am just wondering what most c programmers do when they want to zero out memory. For example I have a buffer of 1024 bytes. Sometimes I do this: char buffer[1024] = {0}; Which will zero all bytes. However, should I declare like this and use memset? char buffer[1024]; . . memset(buffer, 0, sizeof(buffer); Is there any real reason you have to zero the memory? What is the worst that can happen by not doing it? Many thanks for any suggestions,

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  • C++ dynamic array sizing problem

    - by Peter
    The basic pseudo code looks like this: void myFunction() { int size = 10; int * MyArray; MyArray = new int[size]; cout << size << endl; cout << sizeof(MyArray) << endl; } The first cout returns 10, as expected, while the second cout returns 4. Anyone have an explanation?

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  • How can I find out how much memory an instance of a C++ class consumes?

    - by Shadow
    Hi, I am developing a Graph-class, based on boost-graph-library. A Graph-object contains a boost-graph, so to say an adjacency_list, and a map. When monitoring the total memory usage of my program, it consumes quite a lot (checked with pmap). Now, I would like to know, how much of the memory is exactly consumed by a filled object of this Graph-class? With filled I mean when the adjacency_list is full of vertices and edges. I found out, that using sizeof() doesn't bring me far. Using valgrind is also not an alternative as there is quite some memory allocation done previously and this makes the usage of valgrind impractical for this purpose. I'm also not interested in what other parts of the program cost in memory, I want to focus on one single object. Thank you.

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  • Using popen() to invoke a shell command?

    - by Anvar
    When running the following code through xcode I get inconsistent behavior. Sometimes it prints the git version correctly, other times it doesn't print anything. The return code from the shell command is always 0 though. Any ideas on why this might be? What am I doing wrong? #define BUFFER_SIZE 256 int main (int argc, const char * argv[]) { FILE *fpipe; char *command="/opt/local/bin/git --version"; char line[BUFFER_SIZE]; if ( !(fpipe = (FILE*)popen(command, "r")) ) { // If fpipe is NULL perror("Problems with pipe"); exit(1); } while ( fgets( line, sizeof(char) * BUFFER_SIZE, fpipe)) { // Inconsistent (happens sometimes) printf("READING LINE"); printf("%s", line); } int status = pclose(fpipe); if (status != 0) { // Never happens printf("Strange error code: %d", status); } return 0; }

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  • C++ vector and struct problem win32

    - by ~james2432
    I have a structure defined in my header file: struct video { wchar_t* videoName; std::vector<wchar_t*> audio; std::vector<wchar_t*> subs; }; struct ret { std::vector<video*> videos; wchar_t* errMessage; }; struct params{ HWND form; wchar_t* cwd; wchar_t* disk; ret* returnData; }; When I try to add my video structure to a vector of video* I get access violation reading 0xcdcdcdc1 (videoName is @ 0xcdcdcdcd, before I allocate it) //extract of code where problem is video v; v.videoName = (wchar_t*)malloc((wcslen(line)+1)*sizeof(wchar_t)); wcscpy(v.videoName,line); p->returnData->videos.push_back(&v); //error here

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  • finding character in string C language

    - by iSight
    Hi, I am searching a character at first occurence in string using the following code. But, it is taking some time when the character is too long or the character that i am searching is at far extend, which makes delay in other operations. How could i tackle with this problem. The code is below here. Note: attrPtr is a char* which holds a reference to a string containing '"' character at far extend. int position = 0; char qolon = '"';//character to search while (*(attrPtr + position++) != qolon); char* attrValue = NULL; attrValue = (char*)malloc(position * sizeof(char)); strncpy(attrValue, attrPtr, position-1);

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  • Memory allocated with malloc does not persist outside function scope?

    - by PM
    Hi, I'm a bit new to C's malloc function, but from what I know it should store the value in the heap, so you can reference it with a pointer from outside the original scope. I created a test program that is supposed to do this but I keep getting the value 0, after running the program. What am I doing wrong? int f1(int * b) { b = malloc(sizeof(int)); *b = 5; } int main() { int * a; f1(a); printf("%d\n", a); return 0; }

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  • Access violation C++ (Deleting items in a vector)

    - by Gio Borje
    I'm trying to remove non-matching results from a memory scanner I'm writing in C++ as practice. When the memory is initially scanned, all results are stored into the _results vector. Later, the _results are scanned again and should erase items that no longer match. The error: Unhandled exception at 0x004016f4 in .exe: 0xC0000005: Access violation reading location 0x0090c000. // Receives data DWORD buffer; for (vector<memblock>::iterator it = MemoryScanner::_results.begin(); it != MemoryScanner::_results.end(); ++it) { // Reads data from an area of memory into buffer ReadProcessMemory(MemoryScanner::_hProc, (LPVOID)(*it).address, &buffer, sizeof(buffer), NULL); if (value != buffer) { MemoryScanner::_results.erase(it); // where the program breaks } }

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  • I need to create a very large array of bits/boolean values. How would I do this in C/C++?

    - by Eddy
    Is it even possible to create an array of bits with more than 100000000 elements? If it is, how would I go about doing this? I know that for a char array I can do this: char* array; array = (char*)malloc(100000000 * sizeof(char)); If I was to declare the array by char array[100000000] then I would get a segmentation fault, since the maximum number of elements has been exceeded, which is why I use malloc. Is there something similar I can do for an array of bits?

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  • Array of datas returning issue, Overwriting

    - by sijith
    Hi, Please help me on this Here i want to save the converted data into new pointers. But everytime the data is overwriting with most recent data. Please check my code TCHAR nameBuffer[256]; //Globally Declared void Caller() { TCHAR* ptszSecondInFile= QStringToTCharBuffer(userName); TCHAR* ptszOutFile=QStringToTCharBuffer(Destinationfilename); } TCHAR *dllmerge::QStringToTCharBuffer( QString buffer ) { memset(nameBuffer, 0, sizeof(nameBuffer)); #if UNICODE _tcscpy_s(nameBuffer, _countof(nameBuffer), buffer.toUtf8()); #else _tcscpy_s(nameBuffer, _countof(nameBuffer), buffer.toLocal8Bit()); #endif _tprintf( _T( "nameBuffer %s\n" ), nameBuffer ); return nameBuffer; } I am gettting ptszSecondInFile and ptszOutFile both same answer. Is it possible to do with TCHAR* nameBuffer[256];

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  • need to loop through a PHP array in JavaScript

    - by user296516
    Hi guys, For example I have a PHP array, such as this one <?php $s= array('a','b','c','d','e','f') ; ?> And I need to loop through it in JavaScript, any ideas how do I do that? for ( i=0 ; i < <?php echo sizeof($s) ?> ; i++) { document.write('<?php echo $s [somehow need to get the 'i' value into here] ?>'); } Any suggestions? Thanks!

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  • Why did this code still work?

    - by bstullkid
    Some old code that I just came across: MLIST * new_mlist_link() { MLIST *new_link = (MLIST * ) malloc(sizeof(MLIST)); new_link->next = NULL; new_link->mapi = NULL; new_link->result = 0; } This was being called to build a linked list, however I noticed there is no statement: return new_link; Even without the return statement there, the list still got built properly. Why did this happen? EDT: Platform: Mandriva 2009 64bit Linux 2.6.24.7-server GCC 4.2.3-6mnb1

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  • assignment from incompatible pointer type

    - by Hristo
    I have set up the following struct: typedef struct _thread_node_t { pthread_t thread; struct thread_node_t *next; } thread_node_t; ... and then I have defined: // create thread to for incoming connection thread_node_t *thread_node = (thread_node_t*) malloc(sizeof(thread_node_t)); pthread_create(&(thread_node->thread), NULL, client_thread, &csFD); thread_node->next = thread_arr; // assignment from incompatible pointer type thread_arr = thread_node; where thread_arr is thread_node_t *thread_arr = NULL; I don't understand why the compiler is complaining. Maybe I'm misunderstanding something.

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  • Getting MATLAB variable (string) from C

    - by Hamming
    Hi! I'm writing a small C application that launchs a Matlab script (.m file). I need to exchange some variables and I don't know how to get an array of chars that exists in Matlab. I'm doing something like this: enter code here result = engGetVariable(ep,"X"); if (!result) { printf ("Error..."); exit -1; } int n = mxGetN(result); char *varx = NULL; memcpy(varx, mxGetData(result),n*sizeof(char)); It doesn't work. Does someone know how to get a Matlab string in C? I've read Matlab documentation about engGetVariable() and the provided example but any of this things clarify me.

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  • Help with memory leak (malloc)

    - by user146780
    I'v followed a tutorial to use OGL tesselaton. In one of the callbacks there is a malloc and it creates a leak every time I render a new frame. void CALLBACK combineCallback(GLdouble coords[3], GLdouble *vertex_data[4], GLfloat weight[4], GLdouble **dataOut) { GLdouble *vertex; vertex = (GLdouble *) malloc(6 * sizeof(GLdouble)); vertex[0] = coords[0]; vertex[1] = coords[1]; vertex[2] = coords[2]; for (int i = 3; i < 6; i++) { vertex[i] = weight[0] * vertex_data[0][i] + weight[1] * vertex_data[0][i] + weight[2] * vertex_data[0][i] + weight[3] * vertex_data[0][i]; } *dataOut = vertex; } I'v tried to free(vertex) but then the polygons did not render. I also tried allocating on the heap then doing delete(vertex) but then the polygon rendered awkwardly. I'm not sure what to do. Thanks

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  • What key concepts and nuances in C++ you know?

    - by Narek
    What kind of key points and concepts should a person know from C++ (and from programming in general) to be considered that he/she possesses C++ (and programming, in general) skills good. e.g. //Even if sizeof(T) may not be equal to 1, this code steps over array elements T v[]; for(T *p = v ; *p != 0 ; p++) cout<<*p<<endl; P.S. I hope by exchanging this info we will help each other to know C++ and programing thechnics better by doing explicit our notion that we got from practice.

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  • I was making this program and the server wont send to the client

    - by crstin
    void CApplication::SendData( const char pBuffer[] ) { if( pBuffer == NULL ) { Log()->Write( ELogMessageType_ERROR, "Cannot send NULL message."); return; } // calculate the size of that data unsigned long messageSize = strlen( pBuffer ); // fix our byte ordering messageSize = htonl( messageSize ); if( isServer == true ) { for( unsigned int i = ESocket_CLIENT0; i < ESocket_MAX; ++i ) { // send the message size if( m_Socket[ i ] > 0 ) { if( send( m_Socket[ i ], (char*)&messageSize, sizeof( messageSize ), 0 ) == SOCKET_ERROR ) { Log()->Write( ELogMessageType_ERROR, "[Application] Send error: %i to socket %i", WSAGetLastError(), m_Socket[ i ] ); continue; } // fix our message size back to host ordering messageSize = ntohl(messageSize); // send the actual message if( send( m_Socket[ i ], pBuffer, messageSize, 0 ) == SOCKET_ERROR ) { Log()->Write( ELogMessageType_ERROR, "[Application] Send error: %i to socket %i", WSAGetLastError(), m_Socket[ i ] ); continue; } Log()->Write( ELogMessageType_MESSAGE, "[Application] SEND: %s", pBuffer ); } } }

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  • how to get the value of an php array in jQuery

    - by user1933824
    i have a PHP code that will obtain the total images of a certain website via CURL, and put it inside an PHP loop. $z=1; for ($i=0;$i<=sizeof($images_array);$i++) { ....<img src = "$images_array[$i]" id="$z"> .. $z++; } a user can then scan through the array with a prev/next button and the current image being shown will be displayed in my $('$current_image').val(1); $.post("curl_fetch.php?url="+ extracted_url, { }, function(response){ $('#loader').html($(response).fadeIn('slow')); $('#current_image').val(1); // insert loop value in .val() when i click a button, i want to get the value of the array, and not the loop value $(function() { $(document).on('click','.submit', function () { var img = $('#current_image').val(); //get the array value, not the loop value alert(img); });}); now, how do i properly get the array value in my $('#current_image').val(1); in Jquery.

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  • Pointers in C with binary file

    - by darkie15
    Hi All, I am reading the contents of the file using fread into an char array. But I am not sure why it is not getting printed in the output. Here is the code: void getInfo(FILE* inputFile) { char chunk[4]; int liIndex; for (liIndex = 0 ; liIndex < 4 ; liIndex++) { fread(chunk, sizeof(char), 4, inputFile); } printf("\n chunk %s", chunk); } Output prints nothing at all. Where am I going wrong? Regards , darkie

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