the usage(head file and other) of sprintf(), fprintf()

sprintf() is for string, while fprintf() is for file.

#include <stdio.h>

int main(void)
{
        int a = -100;
        FILE *fp;
        unsigned char str[10];
        sprintf(str, "%d", a); // str is string ptr.
        printf("str: %s\n", str);
        fp = fopen("/tmp/fprintf.txt", "w+");
        fprintf(fp, "%s\n", str); // fp is a file ptr.
        fclose(fp);
}