GTest：使用 std::function 参数化测试时的 Valgrind 警告

Question

When running the following dummy Google Test program with valgrind (3.14.0), I receive a series of warning messages which leads me to believe there might be something wrong with the way the program is structured. This is the first time I have observed something like this and I believe it is related to the fact that FooTest is parametrized with a std::function instantiation.

#include <functional>

#include "gtest/gtest.h"

using ::testing::TestWithParam;
using ::testing::Values;


namespace
{

int add(int a, int b)
{
    return a + b;
}

int sub(int a, int b)
{
    return a - b;
}

}

class FooTestHarness
    : public TestWithParam<std::function<int(int, int)>> {};

TEST_P(FooTestHarness, FooTest)
{
  // ...
}

INSTANTIATE_TEST_CASE_P(FooInstantiation, FooTestHarness, Values(add, sub));

The following is an excerpt from the (shortened) valgrind ouput:

==20816== Use of uninitialised value of size 8
==20816==    at 0x4C299BD: _itoa_word (in /usr/lib/libc-2.28.so)
==20816==    by 0x4C2D269: vfprintf (in /usr/lib/libc-2.28.so)
==20816==    by 0x4C55AC5: vsnprintf (in /usr/lib/libc-2.28.so)
==20816==    by 0x4C35503: snprintf (in /usr/lib/libc-2.28.so)
==20816==    by 0x13033C: testing::(anonymous namespace)::PrintByteSegmentInObjectTo(unsigned char const*, unsigned long, unsigned long, std::ostream*)
...
==20816== Conditional jump or move depends on uninitialised value(s)
==20816==    at 0x4C299CE: _itoa_word (in /usr/lib/libc-2.28.so)
==20816==    by 0x4C2D269: vfprintf (in /usr/lib/libc-2.28.so)
==20816==    by 0x4C55AC5: vsnprintf (in /usr/lib/libc-2.28.so)
==20816==    by 0x4C35503: snprintf (in /usr/lib/libc-2.28.so)
==20816==    by 0x13033C: testing::(anonymous namespace)::PrintByteSegmentInObjectTo(unsigned char const*, unsigned long, unsigned long, std::ostream*)
...
==20816== Conditional jump or move depends on uninitialised value(s)
==20816==    at 0x4C2E100: vfprintf (in /usr/lib/libc-2.28.so)
==20816==    by 0x4C55AC5: vsnprintf (in /usr/lib/libc-2.28.so)
==20816==    by 0x4C35503: snprintf (in /usr/lib/libc-2.28.so)
==20816==    by 0x13033C: testing::(anonymous namespace)::PrintByteSegmentInObjectTo(unsigned char const*, unsigned long, unsigned long, std::ostream*)
...
==20816== Conditional jump or move depends on uninitialised value(s)
==20816==    at 0x4C2D3BD: vfprintf (in /usr/lib/libc-2.28.so)
==20816==    by 0x4C55AC5: vsnprintf (in /usr/lib/libc-2.28.so)
==20816==    by 0x4C35503: snprintf (in /usr/lib/libc-2.28.so)
==20816==    by 0x13033C: testing::(anonymous namespace)::PrintByteSegmentInObjectTo(unsigned char const*, unsigned long, unsigned long, std::ostream*)
...

This happens for several versions of GTest including the most recent. Can someone diagnose whether this is my fault or a problem with GTest and/or valgrind?

EDIT: in case this is relevant: I'm on Linux and using gcc 8.2.1

Answer 1

I faced this issue a while ago and got it (partially) solved by imlementing operator << for my class. You could do that for std::function<int(int, int)> :

#include <ostream>
#include <functional>

std::ostream& operator<<(std::ostream& os, const std::function<int(int, int)>& myFunction) {
  return os << "Do something you wish to represent your function";
}

Reference: https://github.com/google/googletest/blob/master/docs/advanced.md#teaching-googletest-how-to-print-your-values

Edit : It seems GTest will try to print your parameters using the operator << (which totally makes sense, of course). However, I'm still unsure on how this relates to the use of unitiliased value valgrind catches.