realloc

realloc is used to reallocate the memory dynamically. Suppose I have allocated 7 bytes using the malloc function and now I want to extend it to 30 bytes. What will happen in the background if there is no sequential (continously in a single row) space of 30 bytes in the memory? Is there any error or will memory be allocated in parts? realloc works behind the scenes roughly like this: If there is enough free space behind the current block to fulfill the request, extend the current block and return a pointer to the beginning of the block. Else if there is a large enough free block elsewhere, then

原型： 用法：#include 有些编译器需要#include 功能：改变mem_address所指内存区域的大小为newsize长度。 说明：如果重新分配成功则返回指向被分配内存的指针，否则返回空指针NULL。 当内存不再使用时，应使用free()函数将内存块释放。 注意：这里原始内存中的数据还是保持不变的。 详细说明及注意要点 1、如果有足够空间用于扩大mem_address指向的内存块，则分配额外内存，并返回mem_address 。这里说的是“扩大”，我们知道，realloc是从堆上分配内存的，当扩大一块内存空间时， realloc()试图直接从堆上现存的数据后面的那些字节中获得附加的字节，如果能够满足，自然天下太平。也就是说，如果原先的内存大小后面还有足够的空闲空间用来分配，加上原来的空间大小＝ newsize。那么就ok。得到的是一块连续的内存。 2、如果原先的内存大小后面没有足够的空闲空间用来分配，那么从堆中另外找一块newsize大小的内存。 并把原来大小内存空间中的内容复制到newsize中。返回新的mem_address指针。（数据被移动了）。老块被放回堆上。 例如： 3、返回情况 返回的是一个void类型的指针，调用成功。（这就在你需要的时候进行强制类型转换） 返回NULL，当需要扩展的大小（第二个参数）为0并且第一个参数不为NULL，此时原内存变成了

This question already has an answer here: Facing an error “*** glibc detected *** free(): invalid next size (fast)” 2 answers I'm having a problem with the realloc function. I'm using C only (so no vector) with LibCurl. The problem I'm having is that I'm getting the following error (realloc(): invalid next size) on the 12th iteration of the write_data function (the function I pass to Curl as a callback, it is called each time libcurl has some data to pass back (data is passed in chunks) ). Trace: -Removed- Source: #include <stdio.h> #include <stdlib.h> #include <curl/curl.h> #include <string.h

I need to implement a simple dynamic array of pointers to a typedef'ed pointer. Using realloc each time it's requested by the user, the array size will grow by sizeof(pointer). So what I have is this: #include <stdio.h> #include <string.h> #include <stdlib.h> typedef void* node; void printmem(node* a, int c) { int i; for (i = 0; i < c; ++i) { printf("%d\t\t%p\n", i, a[i]); } } int main(void) { node* nodes = NULL; int i = 0, count = 20; for (i = 0; i < count; ++i) { nodes = realloc(nodes, sizeof(node)); } printf("Done reallocating\n"); printmem(nodes, i); // free(a); return 0; } This gives the

I'm kinda new to C sorry if my questions is somewhat vague; I need to use realloc on a 2D array without losing it's previous data, I have this function in my program to do it: void modifyMatrix(int **iMat, int iRow, int iRow2, int iCol) { int i; iMat = (int**)realloc(iMat, (iRow2)*sizeof(int*)); for(i=iRow; i<iRow2; i++) { iMat[i]=NULL; } for(i=0; i<iRow2; i++) { iMat[i]=(int*)realloc(iMat[i], (iCol)*sizeof(int)); } } Where iRow is the original size and iRow 2 & iCol are the new size and are all being captured elsewhere in the program. Whenever I try to print the matrix I keep getting junk

int getmin(int a, int b) { return a<b?a:b; } void *reallocation(void *ptr, size_t size) //size_t in bytes { void *newptr; int msize; msize = getsize(ptr); msize = getmin(msize, size); printf("msize = %d", msize); newptr = malloc(size); newptr = memcpy(newptr, ptr, msize); free(ptr); return newptr; } I have implemented my own realloc, and in order to get the size of the allocated memory using malloc(however i know there isn't any method for this in c). My reallocation function is working fine on my system How do we get the size of the memory allocated by malloc(). Also can we do inplace

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 **) realloc(result, sizeof(char *) * (n + 1)); /* nulled but not freed upon failure */ result[n++] = strdup(snd

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 reallocs to defragment the memory, and somehow move ptr2 ? http://opengroup.org/onlinepubs/007908775/xsh