Learn point C language (23): Data type

C Language memory allocation is simple: malloc, calloc, realloc, free

malloc (number of bytes); Returns the first address of the memory segment, void.

Calloc (number, type size); The difference with malloc is that it initializes the memory to be empty.

ReAlloc (original pointer, number of bytes); Reallocation of memory allocated by malloc, calloc; There are too many things to note here:

1, if reduced, will cut off a piece, will retain the previous content;

2, if expanded, will still retain existing content, but the new memory will not initialize;

3, in the expansion, it is possible that the memory address will change, so that the original pointer will be discarded, but the return value is a new pointer, so continue to use should be the return value.

If the allocation fails, it returns NULL, typically because of insufficient memory; Allocating 0 bytes of memory also returns NULL but that doesn't make sense.

They are all freed with free (pointers).

1. Allocate memory to an integer:

#include　<stdio.h>
#include　<stdlib.h>

int　main(void)
{
　　int　*p　=　NULL;

//　　p　=　malloc(sizeof(int));　/*　应该像下一句同时类型转换,　不然在　C++　里面不行　*/
　　p　=　(int　*)malloc(sizeof(int));

　　*p　=　100;
　　printf("%d\n",　*p);

　　free(p);

　　getchar();
　　return　0;
}

2. Allocate memory to 3 integers:

#include　<stdio.h>
#include　<stdlib.h>

int　main(void)
{
　　int　*p　=　NULL;

　　p　=　(int　*)malloc(sizeof(int)*3);

　　*p　=　111;
　　*(p+1)　=　222;
　　*(p+2)　=　333;

　　printf("%d,%d,%d\n",　*p,　*(p+1),　*(p+2));

　　free(p);
　　getchar();
　　return　0;
}