Convert MFC CString to integer

Question

How to convert a CString object to integer in MFC.

Answer 1

The simplest approach is to use the atoi() function found in stdlib.h:

CString s = "123";
int x = atoi( s );

However, this does not deal well with the case where the string does not contain a valid integer, in which case you should investigate the strtol() function:

CString s = "12zzz";    // bad integer
char * p;
int x = strtol ( s, & p, 10 );
if ( * p != 0 ) {
   // s does not contain an integer
}

Answer 2

A _ttoi function can convert CString to integer, both wide char and ansi char can work. Below is the details:

CString str = _T("123");
int i = _ttoi(str);

Answer 3

You may use the C atoi function ( in a try / catch clause because the conversion isn't always possible) But there's nothing in the MFC classes to do it better.

Answer 4

you can also use good old sscanf.

CString s;
int i;
int j = _stscanf(s, _T("%d"), &i);
if (j != 1)
{
   // tranfer didn't work
}

Answer 5

The canonical solution is to use the C++ Standard Library for the conversion. Depending on the desired return type, the following conversion functions are available: std::stoi, std::stol, or std::stoll (or their unsigned counterparts std::stoul, std::stoull).

The implementation is fairly straight forward:

int ToInt( const CString& str ) {
    return std::stoi( { str.GetString(), static_cast<size_t>( str.GetLength() ) } );
}

long ToLong( const CString& str ) {
    return std::stol( { str.GetString(), static_cast<size_t>( str.GetLength() ) } );
}

long long ToLongLong( const CString& str ) {
    return std::stoll( { str.GetString(), static_cast<size_t>( str.GetLength() ) } );
}

unsigned long ToULong( const CString& str ) {
    return std::stoul( { str.GetString(), static_cast<size_t>( str.GetLength() ) } );
}

unsigned long long ToULongLong( const CString& str ) {
    return std::stoull( { str.GetString(), static_cast<size_t>( str.GetLength() ) } );
}

All of these implementations report errors through exceptions (std::invalid_argument if no conversion could be performed, std::out_of_range if the converted value would fall out of the range of the result type). Constructing the temporary std::[w]string can also throw.

The implementations can be used for both Unicode as well as MBCS projects.