c++的c风格字符串函数的实现

　　要注意使用断言判断传入的字符串非空。

#include <cassert>

//求字符串长度
size_t StrLen(const char *str)
{
    assert(str != nullptr);
    size_t len = 0;
    while (*str++ != '')
    {
        ++len;
    }
    return len;
}


//复制字符串
char* StrCpy(char *dest, const char *src)
{
    assert(dest != nullptr && src != nullptr);
    char *temp = dest;
    while ((*dest++ = *src++) != '');
    return temp;
}

//复制指定长度字符串
char* StrNCpy(char *dest, const char *src, size_t n)
{
    assert(dest != nullptr && src != nullptr);
    char *temp = dest;
    size_t i = 0;
    while (i++ < n && (*dest++ = *src++) != '');
    if (*dest != '')
    {
        *dest = '';
    }
    return temp;
}

//比较字符串
int StrCmp(const char *lhs, const char *rhs)
{
    assert(lhs != nullptr && rhs != nullptr);
    int ret = 0;
    while (!(ret = *(const unsigned char *)lhs - *(const unsigned char *)rhs) && *rhs)
    {
        ++lhs;
        ++rhs;
    }
    if (ret > 0)
    {
        return 1;
    }
    else if (ret < 0)
    {
        return -1;
    }
    else
    {
        return 0;
    }
}

//拼接字符串
char* StrCat(char *dest, const char *src)
{
    assert(dest != nullptr && src != nullptr);
    char *temp = dest;
    while (*dest != '')
    {
        ++dest;
    }
    while ((*dest++ = *src++) != '');
    return temp;
}

//附：实现memcpy()函数
void* MemCpy(void *dest, const void *src, size_t n)
{
    assert(dest != nullptr && src != nullptr);
    //不可直接对void类型的指针进行操作
    char *temp_dest = (char*)dest;
    const char *temp_src = (char*)src;
    while (n--)
    {
        *temp_dest++ = *temp_src++;
    }
    return dest;
}

//附2：实现memset()函数
void* MemSet(void *buffer, int c, size_t n)
{
    assert(buffer != nullptr);
    char *temp = (char*)buffer;
    while (n--)
    {
        *temp++ = (char)c;
    }
    return buffer;
}