Unresolved symbols in static library compiled with gcc?

If you're planning on using a C++ library to interface with C, it's important that you mark the functions that the C program will be calling are marked appropriately.

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I am trying to compile some legacy C/C++ code on Mac OS X with gcc 4.2. That was originally written on Windows using Visual Studio. I am compiling a static library that is being linked against by other code, but I've been encountering some hard to understand linker errors. When I try to compile some source code against the static library, the linker gives me the following errors: Undefined symbols for architecture i386: "_read_float", referenced from: _sub_token_values in libcompengine.

A(alparce. O) The method read_float is in the library, and it is being compiled. But when I dump the symbols in the library using nm, I see that under libcompengine.

A(alparce. O) the method _read_float appears as undefined: U _read_float And further down in the file where read_float is supposed to be defined, it appears with a mangled name: 00000686 t __ZL10read_floatPKj Can anyone give me any hints as to why this method isn't being resolved correctly? I spent half a day trying various gcc compiler and source flags, but unfortunately, I haven't hit on a winning combination yet.

C++ gcc g++ linker-error link|improve this question edited Aug 2 '11 at 21:41Kerrek SB63.6k768155 asked Aug 2 '11 at 21:32Greg K162.

If you're planning on using a C++ library to interface with C, it's important that you mark the functions that the C program will be calling are marked appropriately. I've done the following (though there are other ways of doing it) #ifndef INCLUDE_FILE_NAME_H #define INCLUDE_FILE_NAME_H // Insert this before any global function defintitions #ifdef __cplusplus extern "C" { #endif float read_float(); // Insert after all global function defintions #ifdef __cplusplus } #endif #endif What this does is it tells the compiler that all of the external function definitions between the extern "C" {} lines should use C linkage. It only adds the extra definition when compiled with C++.

Another option is to do something like the below, which basically lets you specify function-by-function which should use C linkage, and which don't. #ifdef __cplusplus #define C_LINKAGE "C" #else #define C_LINKAGE #endif extern C_LINKAGE float read_float().

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