1 = false and 0 = true?

Question

I came across an is_equals() function in a c API at work that returned 1 for non-equal sql tables (false) and 0 for equal ones (true). I only realized it after running test cases on my code, one for the positive example and one for the negative and they both failed which at first made little sense. The code in the API does not have a bug as the output was recorded correctly in its documentation. My questions - are there upside down worlds / parallel universes / coding languages where this logical NOTing is normal? Isn't 1 usually true? Is the coder of the API making an error?

Answer 1

For a boolean variable , YES, 1 = true and 0 = false

BUT.... typically the return value of the function is ZERO, if the function completed it's

task successfully and everything worked ok...

But upon error, if something goes wrong, the function returns a NON-ZERO value,

which indicated what happened during the execution of the function. That way, the

API is designed so that the cause of the error can be identified, allowing for trouble

shooting and debugging.

Think of it like this.....

//I am going to call the function to DoSomething() ....

int iReturn = DoSomething();

WAS THERE AN ERROR???? 0 = no error, everything was fine

Non-zero means something happened, something went wrong...

IT is pretty much an industry standard that zero is returned on success

Answer 2

Prior to C99 C had no built in boolean type. C99 added this with an internal "_Bool" type and by adding the #include <stdbool.h> this becomes typedefed to "bool" in congruence with how boolean types are declared in C++.

Conditional statements in C prior to C99 such as "if" blocks simply evaluate if the operand inside is anything other than zero (interpreted to mean "true") and do not if the operand is zero. There's no law saying you can't develop an entire API where literal 1 is defined to mean "false" and 0 is defined to mean "true" except that expressions like if (is_equals(... )) { .... will surely not do what the API user expects, as to their reasoning only they could tell you.

Since C has no native exception system/error handling it's often common to return a value of zero from a function returning int, to mean "EXIT_SUCCESS" and some other int as an error code, for some kind of operation like opening a file, say, or the return value required from all "main" entry point functions for C programs. What returning a shorthand for "EXIT_SUCCESS" means in the context of a comparison function like "is_equals()" is confusing, but perhaps they were aiming for internal logical consistency in their API if all functions return either 0 to indicate success or something else if something went wrong.

If it looks like that's what they did then it would probably be a good idea to see if the API defines a macro for universal function success, or define yourself #define EXIT_SUCCESS (0) and always use that for conditionals when dealing with this API e.g. if (EXIT_SUCCESS == is_equals(... )) {....