For reasons that are not worth mentioning, I want to know if there's a standard defined value for boolean expressions. E.g.
int foo () {
return (bar > 5);
}
The context is that I'm concerned that our team defined TRUE as something different than 1, and I'm concerned that someone may do:
if (foo() == TRUE) { /* do stuff */ }
I know that the best option would be to simply do
if (foo())
but you never know.
Is there a defined standard value for boolean expressions or is it up to the compiler? If there is, is the standard value something included in C99? what about C89?
An operator such as ==, !=, &&, and || that results in a boolean value will evaluate to 1 of the expression is true and 0 if the expression is false. The type of this expressing is int.
So if the TRUE macro is not defined as 1, a comparison such as the above will fail.
When an expression is evaluated in a boolean context, 0 evaluates to false and non-zero evaluates to true. So to be safe, TRUE should be defined as:
#define TRUE (!0)
As was mentioned in the comments, if your compiler is C99 compliant, you can #include <stdbool.h> and use true and false.
According to C99:
6.5.3.3 (Unary arithmetic operators)
The result of the logical negation operator ! is 0 if the
value of its operand compares unequal to 0, 1 if the value of its
operand compares equal to 0. The result has type int. The
expression !E is equivalent to (0==E).
6.5.8 (Relational operators)
Each of the operators < (less than), > (greater than), <=
(less than or equal to), and >= (greater than or equal to)
shall yield 1 if the specified relation is true and 0 if it is false.
The result has type int.
6.5.9 (Equality operators)
The == (equal to) and != (not equal to) operators are
analogous to the relational operators except for their lower
precedence. Each of the operators yields 1 if the specified
relation is true and 0 if it is false. The result has type
int.
6.5.13 (Logical AND operator)
The && operator shall yield 1 if both of its operands compare
unequal to 0; otherwise, it yields 0. The result has type int.
6.5.14 (Logical OR operator)
The || operator shall yield 1 if either of its operands compare
unequal to 0; otherwise, it yields 0. The result has type int.
The C programming language does not define Boolean value. Traditionally, the C programming language uses integer types to represent boolean data types.
Boolean values in C:
0 = false`
Any other value = true`
Usually people will use 1 for true.
C99 introduced the_Bool data type that is not available in other C derivates.See wikipedia link here. Additionally, a new header stdbool.h has been added for compatibility reasons. This header allows programmers to use boolean types in the same way, as in C++ language.
To use bool in C, we can use enum as below.
enum bool {
false, true
};
bool value;
value = bool(0); // False
value = bool(1); // True
if(value == false)
printf("Value is false");
else
printf("Value is true");
Also, related Stack overflow question
Is bool a native C type?
