How can I force a compile error in C++?

Question

I would like to create a compile-time error in my C++ code with a custom error message. I want to do this for a couple of reasons:

to force compilation to fail while I'm working on new features which haven't been implemented yet. (compile time ! TODO reminder)
to create a more readable error when attempting to implement an unsupported template specialization.

I'm sure there is a trick to doing this but I cant find a resource explaining the method. I would wrap the code in a #define of the form COMPILE_FAIL("error message");

Thanks D

What you need is `static_assert`. http://stackoverflow.com/questions/6765770/compile-time-assertion — legends2k, Jan 31 '13 at 19:54

score 43 · Answer 1 · answered Jan 31 '13 at 19:53

43

Use #error:

#error "YOUR MESSAGE"

This produces an error from the preprocessor. If you want to detect an error at a later stage (e.g. during template processing), use static_assert (a C++11 feature).

answered Jan 31 '13 at 19:53

nneonneo

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score 26 · Answer 2 · answered Jan 31 '13 at 20:01

Look into static_assert.

Example:

#include <iostream>
#include <type_traits>

template<typename T>
class matrix {
    static_assert(std::is_integral<T>::value, "Can only be integral type");
};

int main() {
    matrix<int*> v; //error: static assertion failed: Can only be integral type
}

score 5 · Answer 3 · answered Jan 31 '13 at 19:53

5

To force a compiler error (GCC, Clang style):

#error "You ain't finished this yet!"

answered Jan 31 '13 at 19:53

How can I force a compile error in C++?

3 Answers3