gcc 5.40 doesn't include standard include files?

Question

gcc 5.4.0 cygwin 2.8.0 Win10

I've been been knocking my head around this problem.When I compile a simple program, see below, I get an error in one of the gcc include files. I checked the cygwin mailing list and no one has reported an error in the gcc download so I think it's a misunderstanding on my part but I can't figure what I did wrong. Prior to this point all the gcc include fileswere included automatically. Oh, and the compile is correct for other libraries.

The code is:

gcc -std=c++11 test.cpp or gcc test.cpp

include iostream

using namespace std;

int main(int argc, char** argv) { }

and the error message is:

/tmp/ccfBvaqg.o:test.cpp:(.text+0x44): undefined reference to std::ios_base::Init::Init()' /tmp/ccfBvaqg.o:test.cpp:(.text+0x44): relocation truncated to fit: R_X86_64_PC32 against undefined symbolstd::ios_base::Init::Init()'

/tmp/ccfBvaqg.o:test.cpp:(.rdata$.refptr._ZNSt8ios_base4InitD1Ev[.refptr._ZNSt8ios_base4InitD1Ev]+0x0): undefined reference to `std::ios_base::Init::~Init()'

It has nothing to do with include files, it's a linking error. And fact is you didn't link against standard c++ library (-lstdc++). — spectras
– spectras, Commented Jun 22, 2017 at 22:40
Possible duplicate of What is an undefined reference/unresolved external symbol error and how do I fix it? — Ken White
– Ken White, Commented Jun 22, 2017 at 22:46
That's not valid code. C++ code does not start with gcc -std, include has a hash (pound sign) in front of it and the filename is wrapped in <>. In addition, this is a duplicate, which you would have learned if you'd searched here for undefined reference before posting. (And BTW, code isn't formatted with blockquotes; it's formatted as code. Select it and hit Ctrl+K on your keyboard or click the {} button on the toolbar.) — Ken White
– Ken White, Commented Jun 22, 2017 at 22:48

eerorika · Accepted Answer · 2017-06-22 23:41:23Z

1

gcc is the C compiler driver. The compiler automatically detects the language based on the file name; that is why the compilation succeeded. However, the linker is not affected by the names of the source files. By default, the C compiler driver does not link with the C++ standard library.

Since you used the standard library (<iostream> is a bit atypical header file in such a way that merely including it causes a standard library function to be called at the start of the program), but did not link it, the linker fails. The solution is to link with the C++ standard library. The simplest way to do that is to use the C++ compiler driver (g++) which links the standard library by default.

edited Jun 22, 2017 at 23:41

answered Jun 22, 2017 at 23:34

eerorika

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