c语言中strncat函数、函数原型、头文件

1、函数原型

#include <stdio.h>

char *strncat(char *s1, const char *s2, size_t n)
{
    char *tmp = s1;
    
    while(*s1)
        s1++;
    
    while(n--)
    {
        if(!(*s1++ = *s2++))
            break;
    }
    *s1 = '';
    return tmp;
}

int main(void)
{
    char str1[128] = "abcd";
    char str2[128];
    printf("str2: "); scanf("%s", str2);
    unsigned n;
    printf("n = "); scanf("%u", &n);
    
    strncat(str1, str2, n);
    
    printf("concatenate result: %s
", str1);
    return 0;
}

2、头文件

#include <stdio.h>
#include <string.h>

int main(void)
{
    char str1[128] = "abcd";
    char str2[128];
    printf("str2: "); scanf("%s", str2);
    
    unsigned n;
    printf("n = "); scanf("%u", &n);
    
    strncat(str1, str2, n);
    
    printf("concatenate result: %s
", str1);
    return 0;
}