本文共 1812 字，大约阅读时间需要 6 分钟。

模拟实现strlen

int my_strlen(const char* str){    int count = 0;    while (*str)    {        count++;        str++;    }    return count;}

模拟实现strcpy

char* my_strcpy(char* dst, char* src){    assert(dst);    assert(src);    char *p = dst;    while ((*dst++ = *src++))    {        ;    }    return p;}

模拟实现strcat

char* my_strcat(char* dst, const char* src){    assert(src);    assert(dst);    char* p = dst;    while (*dst++)    {        dst++;    }    while ((*dst++ = *src++))    {        ;    }    return p;}

模拟实现strstr

char* my_strstr(const char*str1, const char* str2){    assert(str1);    assert(str2);    char* p1 = str1;    char* p2 = str2;    char* s = NULL;    if (*str2 == '\0')        return NULL;    while (*p1)    {        s = p1;        p2 = str2;        while (*s && *p2 && (*p2 == *s))        {            s++;            p2++;        }        if (*p2 == '\0')            return p1;        p1++;    }}

模拟实现strcmp

int my_strcmp(const char* str1, const char* str2){    int ret = 0;    while (!(ret = *(unsigned char*)str1 - *(unsigned char*)str2) && *str1)    {        ++str1;        ++str2;    }    if (ret < 0)        ret = -1;    if (ret>0)        ret = 1;    return ret;}

模拟实现memcpy

void* memcpy(void* dst,void* src,size_t n){    char* d = dst;    const char* s = src;    while (n--)    {        *d++ = *s++;    }    return dst;}

模拟实现memmove

void* memmove(void* dst, void* src, size_t n){    void* d = dst;    if (dst <= src || (char*)dst >= ((char*)src + n))    {        while (n--)        {            *(char*)dst = *(char*)src;            dst = (char*)dst + 1;            src = (char*)src + 1;        }    }    dst = (char*)dst + n - 1;    src= (char*)src + n - 1;     while (n--)    {        *(char*)dst = *(char*)src;        dst = (char*)dst - 1;        src = (char*)src- 1;    }    return d;}

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