bool to int conversion

Question

How portable is this conversion  Can I be sure that both assertions pass   int x   4 lt 5  assert x  1    x   4 gt 5  assert x  0     Don t ask why  I know that it is ugly  Thank you

User · Accepted Answer

int x   4 lt 5    Completely portable  Standard conformant  bool to int conversion is implicit     4 7 4 from the C   Standard says  Integral Conversion      If the source type is bool  the value false is converted to zero and   the value true is converted to one      As for C  as far as I know there is no bool in C   before 1999  So bool to int conversion is relevant in C   only  In C  4 lt 5 evaluates to int value  in this case the value is 1   4 gt 5  would evaluate to 0   EDIT  Jens in the comment said  C99 has  Bool type  bool is a macro defined in stdbool h header file  true and false are also macro defined in stdbool h     7 16 from C99 says      The macro bool expands to  Bool            true which expands to the integer constant 1  false   which expands to the integer constant 0

User · Answer

Section 6 5 8 6 of the C standard says      Each of the operators  lt   less than        greater than    lt    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

User · Answer

There seems to be no problem since the int to bool cast is done implicitly  This works in Microsoft Visual C    GCC and Intel C   compiler  No problem in either C or C

User · Answer

You tagged your question  C  and  C    at the same time  The results will be consistent between the languages  but the structure of the the answer is different for each of these languages   In C language your examples has no relation to bool whatsoever  that applies to C99 as well   In C language relational operators do not produce bool results  Both 4  gt  5 and 4  lt  5 are expressions that produce results of type int with values 0 or 1  So  there s no  bool to int conversion  of any kind taking place in your examples in C    In C   relational operators do indeed produce bool results  bool values are convertible to int type  with true converting to 1 and false converting to 0  This is guaranteed by the language   P S  C language also has a dedicated boolean type  Bool  macro-aliased as bool   and its integral conversion rules are essentially the same as in C    But nevertheless this is not relevant to your specific examples in C  Once again  relational operators in C always produce int  not bool  results regardless of the version of the language specification

[c++] bool to int conversion

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