calloc

堆和栈的区别： 栈的特征 执行的速度相对较快； 空间较小； 生存期由系统决定； 作用域较小； 有名空间，可以通过变量名或者数据名访问； 堆的特征 执行的速度相对较慢； 空间较大； 生存期由“自己”决定，malloc申请，free释放； 作用域很大（整个程序都可以访问）； 无名空间，只能通过指针使用； C语言空间的申请 malloc 功能： 分配 size 字节的未初始化内存。若分配成功，则返回指向分配内存块最低位（首位）字节的，为任何拥有基础对齐的对象类型对齐的指针。 头文件： #include<stdlib.h> 原型： void* malloc( size_t size ); 参数： size - 要分配的字节数 返回值： 成功时：返回指向新分配内存的指针。为避免内存泄漏，必须用 free() 或 realloc() 解分配返回的指针。 失败时：返回空指针。 说明： malloc申请的空间为连续空间；malloc申请的是没有初始化的空间； 返回值类型是void * 该类型表明malloc返回的地址空间中的数据类型是不确定，必须经过强制类型转换才可以使用。 realloc 功能： 先判断当前的指针是否有足够的连续空间，如果有，扩大mem_address指向的地址，并且将mem_address返回，如果空间不够，先按照newsize指定的大小分配空间

I have an array of array with negative index. It is an array which has real dimensions [dim_y + 40][dim_x + 40] but the user uses the array like it has dimensions [dim_y][dim_x]. First i had global and already defined the dimensions dim_x, dim_y, so i had this int map_boundaries[dim_y + 40][dim_x + 40]; int (*map)[dim_x+40] = (int(*)[dim_x+40])&map_boundaries[20][20]; It worked fine. Now i need the dimensions dim_y and dim_x to be variable, and with this i mean that i want the array 'map' to not have fixed size but dynamic, i need to read the dim_y, dim_x from a user and the array 'map' to be

This question already has an answer here: free() not deallocating memory? 5 answers I don't know if I am doing something wrong or if my concept is somewhat wrong #include<stdio.h> #include<stdlib.h> int main() { int *p; p=calloc(3,sizeof(int)); p[0]=10; p[1]=15; p[2]=30; printf("\n%d\n%p\n%d\n%p\n%d\n%p\n\n",p[0],p,p[1],p+1,p[2],p+2); free(p); //p=NULL; printf("\n%d\n%p\n%d\n%p\n%d\n%p\n\n",p[0],p,p[1],p+1,p[2],p+2); return 0; } When the 2nd, printf() is run, it shows p[2]=30, whereas p[0]=p[1]=0 (in gcc ubuntu and some arbitary values in Code::Blocks windows). I have 2 questions. Why free()

Possible Duplicate: How do I correctly set up, access, and free a multidimensional array in C? I am trying to dynamically allocate memory for a 2D array using calloc. The columns are fixed as 2 so its only the rows that are dynamic. Here is what I have been trying : unsigned int **pts, rows; int main() { //some code pts = (unsigned int **)calloc(2*rows, sizeof (unsigned int **)); } //The code to access the array : for(k=1;k<=i;k++) { printf("\nX%d=",k); scanf("%d",&pts[k][0]); printf("\nY%d=",k); scanf("%d",&pts[k][1]); } But the problem is, while accessing the array, the program crashes. I am

I am playing around with the c functions malloc and calloc and I have some questions. I want to see if I can use these 2 functions to allocate only physical memory, my mac has 4gb or ram and when I use malloc I can allocate way more than 4gb, which means malloc allocate both physical and virtual memory. I have a couple of questions: is there any function I can use, so that I can only allocate the physical memory (w/o allocating the virtual mem) when calling malloc and calloc and when the pointers return, is there any way I can use the pointers to determine how much physical memory are