CPP Exercises

做一些CPP的练习。不讲究奇技淫巧，不讲究运行速度。以练习C++11的语法和强调代码的可读性为主要目标。

按照标准实现strlen,strcpy,strncpy,strcat,strncat,strcmp

  
size_t strlen1(const char* str)
{
    size_t tmp;
    while(*str++)
        tmp++;
    return tmp;
}
//baddress指针存储了目标数组开始的地址
char* strcpy1(char* dest,const char* src)
{
    if((dest==NULL) ||(src==NULL))
        return NULL;
    auto baddress = dest;
    while(*src!='\0')
        *dest++ = *src++;
    return baddress;
}
char* strncpy1(char* dest,const char* src,size_t count)
{
    if((dest==NULL) ||(src==NULL))
        return NULL;
    auto baddress = dest;
    while(count-- &&(*dest++ = *src++))
        ;
    //根据标准，src复制完后count未到0，应该补上\0
    for (; count-- ; *dest++ = '\0');
    return baddress;
}
char* strcat1(char* dest,const char* src)
{
    //strcpy(dest+strlen(src));
  
    if((dest==NULL) ||(src==NULL))
        return NULL;
    auto baddress = dest;
    while(*dest!='\0')
        dest++;
    while(*dest++ = *src++)
        ;
    return baddress;
}
char* strncat1(char* dest,const char* src,size_t count)
{
      
  
    if((dest==NULL) ||(src==NULL))
        return NULL;
    auto baddress = dest;
    while(*dest!='\0')
        dest++;
    while(count-- &&(*dest++ = *src++))
        ;
    return baddress;
}
  
int strcmp1(const char* lhs,const char* rhs)
{
    if((lhs==NULL) ||(rhs==NULL))
        return NULL;
    while(*lhs==*rhs && *rhs)
    {
        lhs++;
        rhs++;
    }
//标准中规定的是左<右时返回负值，相等时返回0
    if(*lhs<*rhs)
        return -1;
    else if (*lhs==*rhs) {
        return 0; }
    else {
        return 1;
    }
  
}

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