C++基本データ型変換

コード:

#include 
#include 
#include 

/*
      ：2018.06.28
        
*/
#define CHAR_TO_INT(x)  int((x) - '0')
void Show(char *p);
void ShowString(std::string &p);
int StrToInt(const std::string &p);
int main()
{
    using namespace std;
    /*              */
    char        temp;
    char        t[10]           = {0};
    char *      p               = NULL;
    string      str             = "";
    int         mInt            = 0;
    double      mDouble         = 0.0;  
    __int64     mInt64          = 0;

    /*  string      char*   */
    str = "123456";
    p = (char *)str.c_str();
    Show(p);
    str = "789";
    p = (char *)str.data();
    Show(p);
    str = "456";
    str.copy(p,str.length(),0);
    Show(p);
    str = "";

    /*   char*      string  */
    p = "123";
    str = p;
    ShowString(str);
    p = NULL;

    /*  string      char[]  */
    str = "456789";
    //str.data()    str    
    //                          
    strcpy(t,str.data());   
    Show(t);
    memset(t,0,sizeof(t));
    str = "";
    str = "123456";
    int i = 0;
    for (; i < str.length(); i++)
    {
        t[i] = str[i];
    }
    if ( i < sizeof(t))
    {
        t[i+1] = '\0';  //          ‘\0’  
    }
    memset(t,0,sizeof(t));
    str = "";

    /* string     int  double int64 */
    str = "123";
    mInt     = atoi(str.c_str());
    mDouble  = atof(str.c_str());
    mInt64   = _atoi64(str.c_str());
    printf(" int = %d, double = %f, int64 = %llu
",mInt,mDouble,mInt64);
    str = "";
    str = "456";
    mInt     = stoi(str);
    mDouble  = stod(str);
    /*
        string                  
        to_string(val)               val   string
        stoi(str,pos,b)                 str p     int
        stol(str,pos,b)             long
        stoul(str,pos,b)            unsigned long
        stoll(str,pos,b)            long long
        stoull(str,pos,b)           unsigned long long
        stof(str,pos)               float
        stod(str,pos)               double
        stold(str,pos)              long double
    */
    printf(" int = %d, double = %f, int64 = %llu
",mInt,mDouble,mInt64);
    str = "";

    //          
    str = "123456789";
    mInt = StrToInt(str);
    cout <<"StrToInt(str) = "<< mInt << endl;
    str.clear();

    /*  char    int */
    temp = '9';
    cout << " CHAR_TO_INT = "<< CHAR_TO_INT(temp) << endl;

    /*************      FINALLY             *******/
    delete p;
    p = NULL;
    system("pause");
    return 0;
}
void Show(char *p)
{
    std::cout << " char * = ";
    while (*p != NULL)
    {
        std::cout << *p << " ";
        p++;
    }
    std::cout << "
";
}
void ShowString(std::string &p)
{
    std::cout << "string = "<< p.c_str() << std::endl;
}
int StrToInt(const std::string &p)
{
    int i = 0,val = 0,strLenth = p.length();
    //       
    if ( p[0] ==  ' - ' )
        i = 1 ;

    //        
    while (i < strLenth)
    {
        //p[i] - ' 0 ' =        ASCII
        val = val * 10 + ( int )(p[i] - '0');
        i ++ ;                                                                                                                                               
    } 
    if (p[ 0 ] == ' - ' )
        val *= - 1 ;
    return val;
}

出力:///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////)=123456789 CHAR_TO_INT=9任意のキーを押して続行してください...
//////////////////////////////////////////////////////////////////////