Compile-time error corresponding to main function in C++

Question

Here is my compilation command followed by the error message I receive. The link where you can see the code is also attached.

g++ -Wall `root-config --cflags --ldflags --libs` StevenJohnsonDoubleIntegration.cpp

/usr/lib/gcc/i686-redhat-linux/4.9.2/../../../crt1.o: In function `_start':(.text+0x18): undefined reference to `main'

collect2: error: ld returned 1 exit status

Link

C++ != C. Use the tag for the language you're actually using, instead of just grabbing any old tag that seems similar. Tags are meaningful here, and using the proper tag is important. It's also important to make it clear in your question - the title says C and the text says C++, and the tags say both. — Ken White, Jan 30 '15 at 03:23
Post the source code. It seems that you don't have any `main()` function. — Iharob Al Asimi, Jan 30 '15 at 03:23
possible duplicate of [undefined reference to main](http://stackoverflow.com/q/8541594/62576) — Ken White, Jan 30 '15 at 03:24

score 2 · Accepted Answer · edited Jan 30 '15 at 03:31

2

The error undefined reference to main means that at linking time, there was no main() function.

Looking at the example code, there is a comment that says:

Compile with -DTEST_INTEGRATOR to generate this little test program.
Usage: ./integrator <dim> <tol> <integrand> <maxeval>
where = # dimensions, = relative tolerance,
is either 0/1/2 for the three test integrands (see below), and is the maximum # function evaluations (0 for none).

Looking at the code, the main function is excluded from the build unless this symbol is defined.

So, add -DTEST_INTEGRATOR to your command line for compiling. You'll probably also want a -o integrator to make the output called integrator instead of a.out

g++ -DTEST_INTEGRATOR -Wall `root-config --cflags --ldflags --libs` StevenJohnsonDoubleIntegration.cpp -o integrator

edited Jan 30 '15 at 03:31

Iharob Al Asimi

52,653
6
59
97

answered Jan 30 '15 at 03:26

John O'M.

510
4
6

Thanks, I should have been more careful, – Benjamin Jan 30 '15 at 03:49
So, is that true that in general if some code is old using C, it might not be working using C++ commands? – Benjamin Jan 30 '15 at 03:56
It is true that not all C will compile as C++, but usually C can compile as C++ (specifically, C code using features from recent C standard versions that don't exist in C++, or C code using C++ reserved words) . In general I would recommend using a C compiler for C code just to not worry about it.Your issue wasn't a C++ vs C issue though; both allow for conditionally compiled code via preprocessor defines. – John O'M. Jan 30 '15 at 04:10

Compile-time error corresponding to main function in C++

1 Answers1