Is Bool-to-Int Conversion Portable in C and C ?

bool to int Conversion

Consider the following code snippet:

int x = 4 < 5;
assert(x == 1);

x = 4 > 5;
assert(x == 0);

The question arises: is this conversion portable? Can we guarantee that both assertions pass?

Answer:

Yes, this conversion is completely portable and compliant with the C Standard. The explicit conversion from bool to int is implicit in C , as defined in §4.7/4 of the C 11 or 14 Standard, and §7.8/4 of the C 17 Standard.

Specifically, the Standard states: "If the source type is bool, the value false is converted to zero and the value true is converted to one."

Therefore, in the given code:

• 4 < 5 evaluates to true, which is implicitly converted to 1 and stored in x.
• 4 > 5 evaluates to false, which is implicitly converted to 0 and stored in x.

Note for C:

In C, a bool data type is not present. However, C99 introduces the _Bool type, which is a macro defined in the stdbool.h header file. Additionally, true and false are macros that expand to integer constants 1 and 0, respectively.

Therefore, in C:

• 4 < 5 evaluates to the integer value 1.
• 4 > 5 evaluates to the integer value 0.

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