函数名: realloc 
 功  能: 重新分配主存 
 用  法: #include <alloc.h> 
         void *realloc(void *ptr, unsigned newsize); 
 程序例: 
#include <stdio.h> 
 #include <alloc.h> 
 #include <string.h> 
int main(void) 
 { 
    char *str; 
   /* allocate memory for string */ 
    str = malloc(10); 
   /* copy "Hello" into string */ 
    strcpy(str, "Hello"); 
   printf("String is %s\n  Address is %p\n", str, str); 
    str = realloc(str, 20); 
    printf("String is %s\n  New address is %p\n", str, str); 
   /* free memory */ 
    free(str); 
   return 0; 
 }