how to use a .c file to write a test class in google test instead of .cpp file?

Question

I have used googletest for my Android NDK project contain .c files. I have used a test class of the type .cpp to do the same. I want to use .c file instead. I get the following error when I try to use it :

Running main() from gtest_main.cc
[==========] Running 0 tests from 0 test cases.
[==========] 0 tests from 0 test cases ran. (1 ms total)
[  PASSED  ] 0 tests.

How can i solve this?

Answer 1

You cannot use a .c file to write a test class in googletest instead of a .cpp file.

A .c file should contain C language source code and a C/C++ compiler will assume that a .c file is to be compiled as C.

A .cpp file should contain C++ language source code and a C/C++ compiler will assume that a .cpp file is to be compiled as C++.

C and C++ are related but different programming languages. C is much older and simpler than C++. There are no classes in the C language. C++ source code containing classes cannot be compiled as C.

Googletest is a unit-testing framework that is written in C++, not C, and it requires you to write your test code in C++, using the framework classes. Your tests must coded in .cpp (and .h ) files so that the compiler will compile them as C++.

However, you can use googletest to unit-test C code. The C code will be in .c and .h files, but you have to code your unit-tests , as usual, in .cpp and .h files. The C/C++ compiler knows that the .c files are to be compiled as C and the .cpp files are to be compiled as C++.

There is a small complication that you must deal with when you want to #include "some_header.h" in your C++ unit-test code, and some_header.h is one of the C-language header files:

The C++ compiler is going to process some_header.h , and it can process it correctly as long as it knows that some_header.h is a C-language header file . To inform the C++ compiler that some_header.h is a C header, you write this:

extern "C" {
#include "some_header.h"
}

If you don't put extern "C" { ... } around the #include for a C-language header then you will get undefined-symbol errors at linktime.

I suggest that you experiment with a project containing the following three files:

return_one.h

// return_one.h
#ifndef RETURN_ONE_H
#define RETURN_ONE_H

// A C library :)

// A C function that always return 1.
extern int return_one(void);

#endif

return_one.c

// return_one.c
#include "return_one.h"

int return_one(void)
{
    return 1;
}

test_return_one.cpp

// test_return_one.cpp
#include "gtest/gtest.h"
extern "C" {
#include "return_one.h"
}

TEST(t_return_one, returns_1)
{
    EXPECT_EQ(1,return_one());  
}

int main(int argc, char **argv)
{
    ::testing::InitGoogleTest(&argc, argv);
    return RUN_ALL_TESTS();
}

Get this project to compile, link and run with googletest.

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