一篇文章教你用C语言模拟实现字符串函数

#include <stdio.h>
int my_strlen(const char* str) {
	int count = 0;
	while (*str++) {
		count++;
	}
	return count;
}
int main() {
	char str[] = "abcdefg";
	int len = my_strlen(str);
	printf("%d", len);
	return 0;
}

#include <stdio.h>
int my_strlen( const char* str) {
	if (*str == '\0') {
		return 0;
	}
	else {
		return my_strlen(++str) + 1;
	}
}
int main() {
	char str[] = "abcdefg";
	int len = my_strlen(str);
	printf("%d", len);
	return 0;
}

#include <stdio.h>
int my_strlen(const char* str) {
	char* p = str;
	while (*p) {
		p++;
	}
	return p - str;
}
int main() {
	char str[] = "abcdefg";
	int len=my_strlen(str);
	printf("%d", len);
	return 0;
}

#include <stdio.h>
char* my_strcpy(char* dest,const char* sour) {
    char* p=dest;
	while (*dest++ = *sour++) {
		;
	}
    return p;
}
int main() {
	char sur[] = "abcdefg";
	char dest[10] = { 0 };
	printf("%s", my_strcpy(dest,sur));
	return 0;
}

#include <stdio.h>
char* my_strcat(char* str2,const char* str1) {
	char* p = str2;
	while (*str2++){
		;
	}
	str2--;
	while (*str2++ = *str1++) {
		;
	}
	return p;
}
int main() {
	char str1[] = "abcdefg";
	char str2[20]="abc";
	printf("%s", my_strcat(str2, str1));
	return 0;
}

#include <stdio.h>
int my_strcmp( const char* str1,const char* str2) {
	while (*str1++-*str2++==0 && *str1!='\0' && str2!='\0') {
		;
	}
	return *--str1 - *--str2;
}
int main() {
	char str1[] = "abcdefg";
	char str2[] = "bbcdef";
	int a=my_strcmp(str1,str2);
	printf("%d", a);
	return 0;
}

#include <stdio.h>
char* my_strncpy(char* dest,const char* sour,int num) {
	char* p = dest;
	while (num--) {
		if (*sour != '\0') {
			*dest++ = *sour++;
		}
		else {
			*dest++ = '\0';
		}
	}
	return p;
}
int main() {
	char sur[] = "abcdefg";
	char dest[10] = { 0 };
	printf("%s", my_strncpy(dest, sur,10));
	return 0;
}

#include <stdio.h>
char* my_strncat(char* str2,const char* str1,size_t num) {
	char* p = str2;
	while (*str2++){
		;
	}
	str2--;
	while (num--) {
		if (*str1 != '\0') {
			*str2++ = *str1++;
		}
	}
	*str2 = '\0';
	return p;
}
int main() {
	char str1[] = "abcdefg";
	char str2[20]="abc";
	printf("%s", my_strncat(str2, str1,6));
	return 0;
}

#include <stdio.h>
int my_strncmp( const char* str1,const char* str2,size_t num){
	while (num--&& *str1++-*str2++==0 && *str1!='\0'&& str2!='\0') {
		;
	}
	return (*--str1 - *--str2);
}
int main() {
	char str1[] = "abcdefg";
	char str2[] = "bbcdef";
	int a=my_strncmp(str1,str2,5);
	printf("%d", a);
	return 0;
}

#include <stdio.h>
const char* my_strstr(const char* str1, const char* str2) {
	while (*str1) {
		const char* p1 = str1;
		const char* p2 = str2;
		while (*p1++ == *p2++) {
			;
		}
		if (*--p2 == '\0') {
			break;
		}
		else {
			str1++;
		}
	}
	return str1;
}
int main() {
	char str1[] = "abbbcdefg";
	char str2[] = "bcde";
	int len = strlen(str2);
	const char* p = my_strstr(str1, str2);
	while (len--) {
		printf("%c", *p++);
	}
	return 0;
}

#include <string.h> 
#include <stdio.h> 
char* my_strtok(char* str, char* demion)
{
    static char* p_last = NULL;
    if (str == NULL && (str = p_last) == NULL)
    {
        return NULL;
    }
    char* s = str;
    char* t = NULL;
    while (*s != '\0')
    {
        t = demion;
        while (*t != '\0')
        {
            if (*s == *t)
            {
                p_last = s + 1;
                if (s - str == NULL)
                {
                    str = p_last;
                    break;
                }
                *s = '\0';
                return str;
            }
            t++;
        }
        s++;
    }
    return NULL;
}
int main(void)
{
    char str[] = "liusen,lin,lll";
    char* result = NULL;
    result = my_strtok(str, ",");
    printf("%s\n", result);
    result = my_strtok(NULL, ",");
    printf("%s\n", result);
    return 0;
}