C语言详细讲解常用字符串处理函数

#include <stdio.h>
#include <string.h>
size_t my_strlen(const char *str)
{
    size_t len = 0;
    while (*str++ != '\0') {
        len++;
    }
    return len;
}
int main()
{
    char *p = "hello world";
    int len_1 = 0, len_2 = 0;

    len_1 = my_strlen(p);
    len_2 = strlen(p);
    printf("len_1 = %d, len_2 = %d\n", len_1, len_2);
    return 0;
}

#include <stdio.h>
#include <string.h>
char *my_strcat(char *dest, const char *src)
{
    while (*dest != '\0') {
        dest++;
    }
    while (*src != '\0') {
        *dest++ = *src++;
    }
    *dest = '\0';
    return dest;
}
int main()
{
    char p1[20] = "hello ";
    char p2[20] = "hello ";
    char *q = "world";
    my_strcat(p1, q);
    strcat(p2, q);
    printf("p1 = %s, p2 = %s\n", p1, p2);
    return 0;
}

#include <stdio.h>
#include <string.h>
char *my_strcpy(char *dest, const char *src)
{
    while (*src != '\0') {
        *dest++ = *src++;
    }
    *dest = '\0';
    return dest;
}
int main()
{
    char p1[20] = {'\0'};
    char p2[20] = {'\0'};
    char *q = "hello world";
    my_strcpy(p1, q);
    strcpy(p2, q);
    printf("p1 = %s, p2 = %s\n", p1, p2);
    return 0;
}

#include <stdio.h>
#include <string.h>
int my_strcmp(const char *str1, const char *str2)
{
    int ret = 0;
    while ((*str1 != '\0') && (*str1 == *str2)) {
        str1++;
        str2++;
    }
    ret = *str1 - *str2;
    return ret;
}
int main()
{
    char p1[20] = {"hello world"};
    char p2[20] = {"hello aorld"};
    int ret_1, ret_2;
    ret_1 = my_strcmp(p2, p1);
    ret_2 = strcmp(p2, p1);
    printf("ret_1 = %d, ret_2 = %d\n", ret_1, ret_2);
    return 0;
}

#include <stdio.h>
#include <string.h>
void *my_memset(void *str, int c, size_t n)
{
    if (str == NULL) 
        return NULL;
    char *pstr = (char*)str;
    while (n-- > 0) {
        *pstr++ = c ;
    }
    return str;
}
int main()
{
    char p1[20] = {"hello world"};
    char p2[20] = {"hello world"};
    my_memset(p1, '*', 5);
    memset(p2, '*', 5);
    printf("p1 = %s, p2 = %s\n", p1, p2);
    return 0;
}