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我要好offer之 str/mem系列手写代码

2024-07-17 05:33:55   220人阅读

1. str*系列手写代码

a. 一定要注意末尾‘\0‘的处理，切记切记

b. 一定要对输入做有效性判断，多用断言就是了

int Strlen(const char* str) {    assert(str != NULL);    const char* tmp = str;    while (*tmp != ‘\0‘) {        ++tmp;    }    return tmp - str;}char* Strcpy(char* dst, const char* src) {    assert(dst != NULL && src != NULL);    char* tmp = dst;    while (*src != ‘\0‘) {        *tmp++ = *src++;    }    *tmp = ‘\0‘;    return dst;}char* Strncpy(char* dst, const char* src, int len) {    assert(dst != NULL && src != NULL && len >= 0);    char* tmp = dst;    for (; len > 0 && *src != ‘\0‘; --len) {        *tmp++ = *src++;    }    for (; len > 0; --len) {        *tmp ++ = ‘\0‘;    }    return dst;}char* Strcat(char* dst, const char* src) {    assert(dst != NULL && src != NULL);    char* tmp = dst;    while (*tmp != ‘\0‘) {        ++tmp;    }    while (*src != ‘\0‘) {        *tmp++ = *src++;    }    *tmp = ‘\0‘;    return dst;}char* Strncat(char* dst, const char* src, int len) {    assert(dst != NULL && src != NULL && n >= 0);    char* tmp = dst;    while (*tmp != ‘\0‘) {        ++tmp;    }    for (; len > 0 && *src != ‘\0‘; --len) {        *tmp++ = *src++;    }    *tmp = ‘\0‘;    return dst;}int Strcmp(const char* str1, const char* str2) {    assert(str1 != NULL && str2 != NULL);    for (; *str1 == *str2; ++str1, ++str2) {        if (*str1 == ‘\0‘) {            return 0;        }    }    if (*(unsigned char*)str1 < *(unsigned char*)str2) {        return -1;    } else {        return 1;    }}int Strncmp(const char* str1, const char* str2, int len) {    assert(str1 != NULL && str2 != NULL && len >= 0);    for (; len > 0; ++str1, ++str2) {        if (*str1 != *str2) {            return ((*(unsigned char*)str1) < (*(unsigned char*)str2) ? -1 : 1);        } else if (*str1 == ‘\0‘) {            return 0;        }    }    return 0;}char* Strchr(const char* str, int c) {    assert(str != NULL);    const char* tmp = str;    const char ch = (const char)c;    for (; *tmp != ch; ++tmp) {        if (*tmp == ‘\0‘) {            return NULL;        }    }    return (char*)tmp;}char* Strstr(const char* str1, const char* str2) {    assert(str1 != NULL && str2 != NULL);    if (*str2 == ‘\0‘) return str1;    const char* tmp1 = str1;    const char* tmp2 = str2;    int len1 = Strlen(str1);    int len2 = Strlen(str2);    int i = 0;    for (tmp1 = str1; i <= len1 - len2 && *tmp1 != ‘\0‘; ++tmp1, ++i) {        if (*tmp1 != *tmp2)            continue;        const char* cur1 = tmp1;        const char* cur2 = tmp2;                while (*cur1 == *cur2) {            ++cur1;            ++cur2;            if (*cur2 == ‘\0‘) {                return (char*)tmp1;            }        }    }    return NULL;}

 

2. mem系列手写代码

一定要对输入做有效性判断，多用断言就是了

void* Memchr(const void* src, int c, int len) {    assert(src != NULL && len >= 0);    const unsigned char ch = c;    const unsigned char* tmp = (const unsigned char*)src;    for (; len > 0; --len, ++tmp) {        if (*tmp == ch) {            return (void*)tmp;        }    }    return NULL;}int Memcmp(const void* s1, const void* s2, int len) {    assert(s1 != NULL && s2 != NULL);    const unsigned char* tmp1 = (const unsigned char*)s1;    const unsigned char* tmp2 = (const unsigned char*)s2;    for (; len > 0; --len, tmp1++, tmp2++) {        if (*tmp1 != *tmp2) {            return ((*tmp1 < *tmp2) ? -1 : 1);        }    }    return 0;}void* Memcpy(void* dst, const void* src, int len) {    assert(dst != NULL && src != NULL && len >= 0);    char* dstTmp = (char*)dst;    const char* srcTmp = (const char*)src;    for (; len > 0; --len, ++dstTmp, ++srcTmp) {        *dstTmp = *srcTmp;    }    return dst;}void* Memmove(void* dst, const void* src, int len) {    assert(dst != NULL && src != NULL && len >= 0);    char* dstTmp = (char*)dst;    const char* srcTmp = (const char*)src;    if (dstTmp > srcTmp && dstTmp < srcTmp + len) {        for (srcTmp += n, dstTmp += n; len > 0 ; --len, --srcTmp, --dstTmp) {            *dstTmp = *srcTmp;        }    } else {        for (; len > 0; --len, ++srcTmp, ++dstTmp) {            *dstTmp = *srcTmp;        }    }    return dst;}

 

3. atoi函数

 http://www.cnblogs.com/wwwjieo0/p/3687534.html

class Solution {public:    int atoi(const char *str) {        assert(str != NULL);        const char* curr = str;        const int maxRange = 10;        int tmp = 0;        int num = 0;        while(isspace(*curr)) {            ++curr;        }        const char* start = nullptr;        char sign;        if (*curr == ‘-‘ || *curr == ‘+‘) {            sign = *curr;            ++curr;            start = curr;        }  else {            start = curr;        }                while (isdigit(*curr)) {            tmp = num;            num = num * 10 + (*curr - ‘0‘);            ++curr;        }        int len = 0;        if (!isdigit(*curr)) {            len = curr - start;        }        --curr;        if (len > maxRange || num < num - *curr) {            if (sign == ‘-‘) {                return INT_MIN;            } else {                return INT_MAX;            }        }        if (sign == ‘-‘)  num = -num;        return num;    }};

 


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