std::string initialization with a bool

3
votes

Consider the following initialization:

std::string falseString = false;
std::string trueString = true;

With g++ 5.2.0, compiler throws a warning for falseString, while an error for trueString.

With clang++ 3.6 -std=c++11, compiler throws error for both falseString as well as trueString.

Q1) Why the different behavior with gcc even though both initialization values are of the same type (bool)?

Q2) Which compiler is correct and why? What does the standard say?

EDIT:

error: no viable conversion from 'bool' to 'std::string' (aka 'basic_string')

warning: converting 'false' to pointer type for argument 1 of 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(const _CharT*, const _Alloc&) [with _CharT = char; _Traits = std::char_traits; _Alloc = std::allocator]' [-Wconversion-null]

1
c++c++11g++stdstringclang++
Telling us what the warnings/errors are might be a clue...? Did you omit them deliberately? – Lightness Races in Orbit
Mainly historical - stackoverflow.com/questions/32009694/… – Cory Kramer

1 Answers

6
votes

For starters, you definitely cannot initialise a std::string from true. That's just nonsensical.

GCC 5.2 is accepting the initialisation from false, with protest, because it used to be a valid null pointer literal. Yeah. Compare 3.9.1/6 between C++03 and C++11 — "as described below, bool values behave as integral types" was removed.

It should error on both compilers these days, but GCC was buggy in this regard until like a month ago (so GCC 6.0).