why use g++ instead of gcc to compile *.cc files?
I compiled a library which use the g++ instead gcc. First I thought the source code was written in C++ but I found out later that there was not any C++ code in the *.cc files.
To confirm this, I replaced the g++ in the original makefile with gcc. And I still got the correct program.
Anyone can explain this? It was not the first time I met such a situation.
It depends on what exactly you changed in the makefile. gcc / g++ is really just a front-end driver program which invokes the actual compiler and / or linker based on the options you give it.
If you invoke the compiler as gcc :
.c , or .cc / .cpp ); If you invoke the compiler as g++ :
.c or .cc / .cpp ; (see the relevant bit of the GCC documentation).
Here's a simple program which detects whether or not it has been compiled as C or C++.
(It makes use of the fact that a character constant has the size of an int in C, or a char in C++. sizeof(char) is 1 by definition; sizeof(int) will generally be larger - unless you're using an obscure platform with >= 16-bit bytes, which you're probably not.)
I've called it test.c and copied it as test.cc as well:
$ cat test.c
#include <stdio.h>
int main(void)
{
printf("I was compiled as %s!n", sizeof('a') == 1 ? "C++" : "C");
return 0;
}
$ cp test.c test.cc
$
Compiling and linking test.c with gcc , and test.cc with g++ , works as expected:
$ gcc -o test test.c
$ ./test
I was compiled as C!
$ g++ -o test test.cc
$ ./test
I was compiled as C++!
$
Compiling and linking test.cc with gcc doesn't work: it compiles the code as C++ because the file ends in .cc , but fails at the link stage:
$ gcc -o test test.cc
/tmp/ccyb1he5.o:(.eh_frame+0x11): undefined reference to `__gxx_personality_v0'
collect2: ld returned 1 exit status
$
which we can prove by separately compiling with gcc , and linking with g++ (to pull in the right libraries):
$ gcc -c test.cc
$ g++ -o test test.o
$ ./test
I was compiled as C++!
$
... gcc has compiled the code as C++ rather than C, because it had a .cc file extension.
Whereas g++ does not compile .c files as plain C:
$ g++ -o test test.c
$ ./test
I was compiled as C++!
$
It could be that the .cc code happens to be C, but was intended to be linked into a C++ library. The internals are different.
g++ automatically links the C++ runtime library — gcc doesn't. Obvoiusly, when it doesn't matter — then it doesn't matter, but, as already pointed out by spraff, it could be intended for future use.
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