现场编写类似strstr/strcpy/strpbrk的函数

1.strstr

int strstr(char *string, char *substring)      
{     
    if (string == NULL || substring == NULL)        
        return -1;        
      
    int lenstr = strlen(string);     
    int lensub = strlen(substring);     
      
    if (lenstr < lensub)        
        return -1;         
      
    int len = lenstr - lensub;  
    for (int i = 0; i <= len; i++)   //复杂度为O(m*n)      
    {     
        for (int j = 0; j < lensub; j++)     
        {     
            if (string[i+j] != substring[j])     
                break;     
        }     
        if (j == lensub)     
            return i + 1;     
    }     
    return -1;     
} 

2.strcpy

//得10分，基本上所有的情况，都考虑到了   
//如果有考虑到源目所指区域有重叠的情况，加1分！      
char * strcpy( char *strDest, const char *strSrc )      
{     
    if(strDest == strSrc) { return strDest; }  
    assert( (strDest != NULL) && (strSrc != NULL) );     
    char *address = strDest;      
    while( (*strDest++ = * strSrc++) != '/0' );      
    return address;     
}    

3.