When writing/debugging VEX code, you can set the HOUDINI_VEX_ASSERT environment variable, and then use the assert(condition) macro to test invariants in your code.

The benefit of using assert() over printf is that when the environment variable is not set, the condition will not run and the assertions will likely be optimized away. You can leave the asserts in your code and they won’t affect the production performance of your VEX code.

Note that the assert() macro simply prints a message to the console. It does not stop execution of the program.

You must include assert.h at the top of the file to import the assert() macro:

#include "assert.h"

cvex
test_assert(string texture_map="")
{
    assert(1 == 2);
    assert(0 == 0);
    assert(texture_map != "");
}

% export HOUDINI_VEX_ASSERT=1

% vexexec test_assert.vfl
VEX Assertion Failed ./test_assert.vfl:6 - (1 == 2)
VEX Assertion Failed ./test_assert.vfl:8 - (texture_map != "")

% vexexec test_assert.vfl texture_map Mandril.rat
VEX Assertion Failed ./test_assert.vfl:6 - (1 == 2)

The assert_enabled function tests whether the HOUDINI_VEX_ASSERT environment variable is set. You could use that function to write your own assert macro (for example, you might write a macro that used your studio’s logging infrastructure).