Does boolean true ever return 0?

Question

I was in a lecture and on the power point slides states that true would return 0 and false would return 1. I stated that in Visual Studio anything non zero is considered true, but is there a C++ standard that defines 0 as true?

Visual studio's results were disregarded as non standard but I doubt that it is.

bool tru = true; // returns 0
bool fal = false; // returns 1

What version of Visual Studio? Can you provide a complete program that reproduces the behavior? — , Feb 28 '15 at 06:06
I was just checking if the lecture's were wrong. The behaviour in Visual Studio 2013 is 1 == true and 0 == false — Joshua Waring, Feb 28 '15 at 06:14
Are you sure (s)he was talking about functions return values, and not process exit status? — Jean-Baptiste Yunès, Feb 28 '15 at 07:56
There is no return in the example, so it isn't clear what they are referring to. — juanchopanza, Feb 28 '15 at 08:33
In other words, values such as `true` or `false` don't return anything, so the question is meaningless. — juanchopanza, Feb 28 '15 at 09:12

score 5 · Accepted Answer · answered Feb 28 '15 at 06:07

Absolutely not. From the C++14 working draft (chosen here because I was able to find it easily, not because it's specific to C++14):

A prvalue of type bool can be converted to a prvalue of type int, with false becoming zero and true becoming one.

— http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4296.pdf §4.5.6 (page 85)

Indeed, this behavior is common to most programming languages. Off the top of my head, for instance, Perl, Python, PHP, and Javascript all treat 0 as false and nonzero values as true. The only situation I can think of where 0 is "true" is in UNIX shell scripting, where an exit code of 0 is used for success and nonzero values are used for errors.

Every C++ standard - not just C++14 - has specified that converting true to int gives a value 1, and false gives a value 0. — Rob, Feb 28 '15 at 08:22

score 2 · Answer 2 · edited May 23 '17 at 12:08

2

As mentioned in the accepted answer here, true is defined by the standard to compare equal to 1, and false to 0:

(§4.7/4): "If the source type is bool, the value false is converted to zero and the value true is converted to one."

edited May 23 '17 at 12:08

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answered Feb 28 '15 at 06:06

Emil Laine

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Does boolean true ever return 0?

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