C++ – How to add a linker or compile flag in a CMake file

ccmake

I am using the arm-linux-androideabi-g++ compiler. When I try to compile a simple "Hello, World!" program it compiles fine. When I test it by adding a simple exception handling in that code it works too (after adding -fexceptions .. I guess it is disabled by default).

This is for an Android device, and I only want to use CMake, not ndk-build.

For example – first.cpp

#include <iostream>

using namespace std;

int main()
{
   try
   {
   }
   catch (...)
   {
   }
   return 0;
}

./arm-linux-androideadi-g++ -o first-test first.cpp -fexceptions

It works with no problem…

The problem … I am trying to compile the file with a CMake file.

I want to add the -fexceptions as a flag. I tried with

set (CMAKE_EXE_LINKER_FLAGS -fexceptions ) or set (CMAKE_EXE_LINKER_FLAGS "fexceptions" )

and

set ( CMAKE_C_FLAGS "fexceptions")

It still displays an error.

Best Answer

Note: Given CMake evolution since this was answer was written, most of the suggestions here are now outdated/deprecated and have better alternatives

Suppose you want to add those flags (better to declare them in a constant):

SET(GCC_COVERAGE_COMPILE_FLAGS "-fprofile-arcs -ftest-coverage")
SET(GCC_COVERAGE_LINK_FLAGS    "-lgcov")

There are several ways to add them:

  1. The easiest one (not clean, but easy and convenient, and works only for compile flags, C & C++ at once):

     add_definitions(${GCC_COVERAGE_COMPILE_FLAGS})

  2. Appending to corresponding CMake variables:

     SET(CMAKE_CXX_FLAGS  "${CMAKE_CXX_FLAGS} ${GCC_COVERAGE_COMPILE_FLAGS}")
 SET(CMAKE_EXE_LINKER_FLAGS  "${CMAKE_EXE_LINKER_FLAGS} ${GCC_COVERAGE_LINK_FLAGS}")

  3. Using target properties, cf. doc CMake compile flag target property and need to know the target name.

     get_target_property(TEMP ${THE_TARGET} COMPILE_FLAGS)
 if(TEMP STREQUAL "TEMP-NOTFOUND")
   SET(TEMP "") # Set to empty string
 else()
   SET(TEMP "${TEMP} ") # A space to cleanly separate from existing content
 endif()
 # Append our values
 SET(TEMP "${TEMP}${GCC_COVERAGE_COMPILE_FLAGS}" )
 set_target_properties(${THE_TARGET} PROPERTIES COMPILE_FLAGS ${TEMP} )

Right now I use method 2.

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