c语言中strncmp函数，函数原型，头文件

1、函数原型

#include <stdio.h>

int strncmp(const char *s1, const char *s2, size_t n)
{
    while(n && *s1 && *s2)
    {
        if(*s1 != *s2)
            return (unsigned char)*s1 - (unsigned char)*s2;
        n--;
        s1++;
        s2++;
    }
    if(!n)
        return 0;
    if(*s1)
        return 1;
    return -1;
}

int main(void)
{
    char str1[128] = "abcd";
    char str2[128];
    printf("str2: "); scanf("%s", str2);
    
    unsigned n;
    printf("n = "); scanf("%u", &n);
    
    int tmp = strncmp(str1, str2, n);
    if(tmp > 0)
        puts("str1 > str2");
    else if(tmp == 0)
        puts("str1 = str2");
    else
        puts("str1 < str2");
    return 0;
}

 改进

↓

#include <stdio.h>

int strncmp(const char *s1, const char *s2, size_t n)
{
    while(n && *s1 && *s2)
    {
        if(*s1 != *s2)
            return (unsigned char)*s1 - (unsigned char)*s2;
        n--;
        s1++;
        s2++;
    }
    if(!n)
        return 0;
    if(*s1 == *s2)
        return 0;
    if(*s1)
        return 1;
    return -1;
}

int main(void)
{
    char str1[128] = "abcd";
    char str2[128];
    printf("str2: "); scanf("%s", str2);
    
    unsigned n;
    printf("n = "); scanf("%u", &n);
    
    int tmp = strncmp(str1, str2, n);
    if(tmp > 0)
        puts("str1 > str2");
    else if(tmp == 0)
        puts("str1 = str2");
    else
        puts("str1 < str2");
    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);
    
    int tmp = strncmp(str1, str2, n);
    if(tmp > 0)
        puts("str1 > str2");
    else if(tmp == 0)
        puts("str1 = str2");
    else
        puts("str1 < str2");
    return 0;
}