realloc

问题 I use realloc to resize the memory allocated: char **get_channel_name(void) { char **result; int n; result = (char **) 0; for (elem = snd_mixer_first_elem(handle), n = 0; elem; elem = snd_mixer_elem_next(elem)) { if (!snd_mixer_selem_is_active(elem)) continue; if (snd_mixer_selem_has_playback_volume(elem) && snd_mixer_selem_has_playback_switch(elem) && snd_mixer_selem_has_capture_switch(elem)) { if (result == (char **) 0) result = (char **) malloc(sizeof(char *)); else result = (char **)

问题 I am wondering whether the C or C++ standard guarantees that a pointer is not changed when realloc is called with a smaller (nonzero) size: size_t n=1000; T*ptr=(T*)malloc(n*sizeof(T)); //<--do something useful (that won't touch/reallocate ptr of course) size_t n2=100;//or any value in [1,n-1] T*ptr2=(T*)realloc(ptr,n2*sizeof(T)); //<-- are we guaranteed that ptr2==ptr ? Basically, can the OS decide on its own that since we freed a large memory block, he wants to take advantage of all

问题 The realloc reference says: The function may move the memory block to a new location, in which case the new location is returned. Does it mean that if I do this: void foo() { void* ptr = malloc( 1024 ); unsigned char* cptr = ( unsigned char* )ptr+256; ptr = realloc( ptr, 4096 ); } then cptr may become invalid if realloc moves the block? If yes, then does realloc signal in any way, that it will move the block, so that I can do something to prevent cptr from becoming invalid? 回答1: Yes, cptr

问题 How can I realloc in C++? It seems to be missing from the language - there is new and delete but not resize ! I need it because as my program reads more data, I need to reallocate the buffer to hold it. I don't think delete ing the old pointer and new ing a new, bigger one, is the right option. 回答1: Use ::std::vector! Type* t = (Type*)malloc(sizeof(Type)*n) memset(t, 0, sizeof(Type)*m) becomes ::std::vector<Type> t(n, 0); Then t = (Type*)realloc(t, sizeof(Type) * n2); becomes t.resize(n2); If

问题 I am trying to realloc an array of structs when it runs out of space as I'm putting elements into it but I keep receiving a realloc stderr. The array of struct will eventually have 235,000 elements in it. When I set the initial start size to 100,000 I receive the stderr when trying to realloc. If I se the initial start size to 300,000 it does not give the error because it never reaches the realloc statement. #define _XOPEN_SOURCE #include <stdlib.h> #include <stdio.h> #include <assert.h>

问题 If the area pointed to was moved, a free(ptr) is done. Can you please explain the above line about realloc() ? This line is from a man page for calloc, malloc, realloc and free. 回答1: I think this explains it better: If sufficient space does not exist to expand the current block in its current location, a new block of the size for size is allocated, and existing data is copied from the old block to the beginning of the new block. The old block is freed, and the function returns a pointer to

问题 I'm trying to familiarize with QGLViewer (http://libqglviewer.com/) so I installed it (on Ubuntu 14.04) and I'm trying to run the simpleViewer (which is a provided example). Now, the code can be built using qmake, but I want to compile the code with cmake so I wrote the following CMakeLists.txt: cmake_minimum_required(VERSION 2.6) PROJECT(simple_viewer) SET(CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake_modules) FIND_PACKAGE(OpenGL REQUIRED) INCLUDE_DIRECTORIES(${OPENGL_INCLUDE}) FIND_PACKAGE

问题 void replace(char *str) { unsigned int len = 0; unsigned int no_of_spaces = 0; while (*str) { if ((char)*str == SPACE) no_of_spaces++; str++; len++; } unsigned int new_len = len + 2 * no_of_spaces; str = (char*) realloc(str, new_len * sizeof(char)); str[new_len] = '\0'; } I use function like replace("random string"); . Here I am trying to increase the size of the string so that spaces can be replaced with another string. For this I need to count the no of spaces and also get the length of the

问题 Currently trying to write menu based program that asks user for student records, after initial records are entered I want user to have option to add more record slots but when I try to realloc my 2d pointer array my program crashes, specifically after the 2nd function is called. #include <stdio.h> #include <string.h> #include <stdlib.h> #define LENGTH 21 void printRecords(int* size, char **fistName, char **lastName, float *grade); void addRecord(int* size, char** firstName, char** lastName,

问题 I'm pretty new to c, so if my steps are wrong, please let me know. Let's say that I have something like the following: struct graphNode{ int val; graphNode* parent; int succSize; int succMaxSize; graphNode* succ[1]; }; I will create a new node with: graphNode *n; n = malloc(sizeof(struct graphNode)); assert(n); n->val = 1; n->parent = NULL; n->succSize = 0; n->succMaxSize = 1; Then, if I want to add a successor to the node if (n->succSize == n->succMaxSize){ n->succ = realloc(n->succ, sizeof