Add custom messages in assert?

user_444423 0
Viewed 97045

Is there a way to add or edit the message thrown by assert? I'd like to use something like 

assert(a == b, "A must be equal to B");

Then, the compiler adds line, time and so on...

Is it possible?

assert c++
9 Answers

If the assert is done within a class, an alternative approach is to call a static predicate function with a self-describing name. If the assertion fails, the message will already contain the predicate's pretty and self-describing name.

E.g.:

static bool arguments_must_be_ordered(int a, int b) {return a <= b;}

void foo(int a, int b)
{
    assert(arguments_must_be_ordered(a, b));
    // ...
}

You may even want to make that predicate function public so that the class' user can verify the precondition themselves.

Even if assert is not disabled for release builds, the compiler will likely inline the predicate if it's fairly trivial.

The same approach can be used for complex if conditions needing a comment. Instead of a comment, just call a self-describing predicate function.

user_2452650

You could also just write your own custom assert function. A very simple example:

bool print_if_false(const bool assertion, const char* msg) {
    if(!assertion) {
        // endl to flush
        std::cout << msg << std::endl;
    }
    return assertion;
}

int main()
{
    int i = 0;
    int j = 1;
    assert(print_if_false(i == j, "i and j should be equal"));
    return 0;
}

play with the code.

The assertion reads Assertion print_if_false(i == j, "i and j should be equal").

user_53457150
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