c++ std::string to boolean

Question

I am currently reading from an ini file with a key/value pair. i.e.

isValid = true

When get the key/value pair I need to convert a string

Answer 1

Lowercase the string by iterating the string and calling tolower on the carachters, then compare it to "true" or "false", if casing is your only concern.

for (std::string::iterator iter = myString.begin(); iter != myString.end(); iter++)
    *iter = tolower(*iter);

Answer 2

Suggestions for case-insenstive string comparisions on C++ strings can be found here: Case insensitive string comparison in C++

Answer 3

Another solution would be to use tolower() to get a lower-case version of the string and then compare or use string-streams:

#include <sstream>
#include <string>
#include <iomanip>
#include <algorithm>
#include <cctype>

bool to_bool(std::string str) {
    std::transform(str.begin(), str.end(), str.begin(), ::tolower);
    std::istringstream is(str);
    bool b;
    is >> std::boolalpha >> b;
    return b;
}

// ...
bool b = to_bool("tRuE");

Answer 4

#include <string>
#include <strings.h>
#include <cstdlib>
#include <iostream>

bool
string2bool (const std::string & v)
{
    return !v.empty () &&
        (strcasecmp (v.c_str (), "true") == 0 ||
         atoi (v.c_str ()) != 0);
}

int
main ()
{
    std::string s;
    std::cout << "Please enter string: " << std::flush;
    std::cin >> s;
    std::cout << "This is " << (string2bool (s) ? "true" : "false") << std::endl;
}

An example input and output:

$ ./test 
Please enter string: 0
This is false
$ ./test 
Please enter string: 1
This is true
$ ./test 
Please enter string: 3
This is true
$ ./test 
Please enter string: TRuE
This is true
$ 

Answer 5

If you can't use boost, try strcasecmp:

#include <cstring>

std::string value = "TrUe";

bool isTrue = (strcasecmp("true",value.c_str()) == 0);