#include #include // simple example about dynamic memory allocation // (malloc, calloc, realloc, free) /* In this program i'll try to allocate two custom contiguous memory blocks for storing integers. Integer size can vary from one computer to another but here it's 4 bytes so if first integer is stored at address 0000, the subsequents will be stored at 0004, 0008, 0012... (this is a simple explanation, we usually work with values in hexadecimal like in this example). The default allocated values could be: malloc -> random values previously stored in that memory point (sometimes called 'garbage'). calloc -> each memory chunk has the value 0. Resizing each block doesn't imply that address value change, this will occur only in case the contiguous memory is already in use, that is, that memory realloc need already contains some value in use. Also note that if you reallocates a block of memory and doesn't set values, that new memory locations can contain garbage. * This program is simplyfied. Usually you must check that memory allocation process is correct. Eg: int *test = malloc(4 * sizeof(int)); if (test == NULL) { printf("Error allocating memory\n"); exit(0); } */ int main(void) { // variable that I'll reuse in every iteration int i; // allocating a block of memory for 4 integers int *test_m = malloc(4 * sizeof(int)); // allocating and clearing allocated space int *test_c = calloc(4, sizeof(int)); // printing the content of memory before setting printf("malloc default values\n"); for (i = 0; i < 4; i++) printf("%d\n", test_m[i]); // printing the content of memory before setting printf("\ncalloc default values\n"); for (i = 0; i < 4; i++) printf("%d\n", test_c[i]); //setting values to both blocks of memory printf("\nsetting values...\n"); for (i = 0; i < 4; i++) { // storing integer values from 0 to 3 test_m[i] = i; test_c[i] = i; } // printing stored values printf("\nstored values\n"); for (i = 0; i < 4; i++) { printf("test_m[%d] = %d\n", i, test_m[i]); printf("test_c[%d] = %d\n\n", i, test_c[i]); } // printing memory addresses before realloc printf("\nmalloc addresses\n"); for (i = 0; i < 4; i++) printf("%p\n", &test_m[i]); // printing memory addresses before realloc printf("\ncalloc addresses\n"); for (i = 0; i < 4; i++) printf("%p\n", &test_c[i]); printf("\nreallocating...\n"); // resizing down test_malloc test_m = realloc(test_m, 3 * sizeof(int)); // resizing up test_calloc test_c = realloc(test_c, 8 * sizeof(int)); //printing values after realloc printf("\nstored values after realloc\n"); for (i = 0; i < 3; i++) printf("test_m[%d] = %d\n", i, test_m[i]); printf("\n"); for (i = 0; i < 8; i++) printf("test_c[%d] = %d\n", i, test_c[i]); // printing memory addresses after realloc printf("\nmalloc addresses\n"); for (i = 0; i < 3; i++) printf("%p\n", &test_m[i]); // printing memory addresses after realloc printf("\ncalloc addresses\n"); for (i = 0; i < 8; i++) printf("%p\n", &test_c[i]); // freeing memory printf("\nfreeing memory...\n"); free(test_c); free(test_m); printf("\nend of program"); return 0; }