How to print additional information when assert fails?

Question

Often one wants to print out additional information if an assert fails. A way to do that is this:

assert(vec.size() > i || 
  !(std::cerr << "False: " << vec.size() << ">" << i))

This way the actual sizes are printed when the assert fails. But it's ugly, and also it's easy to forget the ! , which will make the assertion condition true and the program will just continue.

What do people use instead to print additional information on assertion failure, like above?

Answer 1

#define ASSERT(condition) { if(!(condition)){ std::cerr << "ASSERT FAILED: " << #condition << " @ " << __FILE__ << " (" << __LINE__ << ")" << std::endl; } }

Usage:

ASSERT(vec.size()>1);

Result:

ASSERT FAILED: vec.size()>1 @ main.cpp (17)

You can optionally put DebugBreak() or exit(-1) or watever into the macro, depending on your needs.

Updated macro with separated left and right side:

#define ASSERT(left,operator,right) { if(!((left) operator (right))){ std::cerr << "ASSERT FAILED: " << #left << #operator << #right << " @ " << __FILE__ << " (" << __LINE__ << "). " << #left << "=" << (left) << "; " << #right << "=" << (right) << std::endl; } }

Usage:

ASSERT(a,>,b);

Result:

ASSERT FAILED: a>b @ assert2.cpp (8). a=3; b=4