将char转换为bool（将bool传递给main）

Question

Is there a recommended/correct/safer way to pass a bool argument to your main function?

Are this

$ ./my_software true

with this as my_software :

int main(argc, argv* []){

    bool my_bool = argv[1];

    return 0;
}

and this

$ ./my_software 1

with this as my_software :

int main(argc, argv* []){

    bool my_bool = atoi(argv[1]);

    return 0;
}

equivalent? Am I missing a conversion in the first one?

Answer 1

C++ streams can handle this. Don't forget to check that argv[1] actually exists !

#include <sstream>
//...
std::stringstream ss(argv[1]);
bool b;

if(!(ss >> std::boolalpha >> b)) {
    // Parsing error.
}

// b has the correct value.

Live on Coliru

Putting in the std::boolalpha stream manipulator enables parsing "true" and "false", leaving it out will let it parse "0" and "1".

Answer 2

As for correct ways to do it, there's a lot. But there are unsafe/incorrect ways that you propose. First you are not guaranteed that argv is of length 2 or higher, you have to check argc before even looking at argv[1] (or anything in argv .

Second you're not guaranteed to get particular content in argv[1] even if it does exist. It could be any string, not only the expected "0" or "1" (it could even be the empty string) so just running it through atoi is probably not a wise choice.

Answer 3

Yes, you're missing a conversion on the first example, and most compilers should issue a diagnostic. The code won't work anyway, even if it compiles, because it tries to convert a raw character pointer to a bool value, and won't even look at the contents of the string.