g++ link problems: In function `_start': (.text+0x20): undefined reference to `main' - c++

Question

I am getting an undefined reference to main error - even though I have defined main, and (AFAICT), I have linked it correctly. Here is my code and the commands I used:
// ################################################
//proj1.h
#ifndef __SCRATCH_PROJ1_H
#define __SCRATCH_PROJ1_H
int addOne(int i);
#endif /*__SCRATCH_PROJ1_H */
// ################################################
//proj1.cpp
#include "proj1.h"
int addOne(int i){
return i+1;
}
// ################################################
//proj1_unittest.cpp
#include "proj1.h"
#include "gtest/gtest.h"
// Test Function
TEST(addOneTest, Positive) {
EXPECT_EQ(1,addOne(0));
EXPECT_EQ(2,addOne(1));
EXPECT_EQ(40320, addOne(40319));
}
TEST(addOneTest, Negative) {
EXPECT_FALSE(addOneTest(-1));
}
GTEST_API_ int main(int argc, char **argv) {
testing::InitGoogleTest(&argc, argv);
return RUN_ALL_TESTS();
}
Here is the console output:
$ g++ -isystem -pthread -c ${SOURCE_DIR}/proj1.c -o ${SOURCE_DIR}/proj1.o
$ g++ -o ${SOURCE_DIR}/mytest ${SOURCE_DIR}/*.o -L${GTEST_DIR} libgtest.a
/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: ld returned 1 exit status
Why is the main() function not been found by the linker?

Answer 1

As far as I can see you are not compiling file proj1_unittest.cpp (as your code comment has it) / proj1_unittest.c (as your console output implies).