undefined reference to `browse'

[nunorpg]

Hello,
I'm having a problem linking a c library to c++ project.
In the build I'm facing the following error..

    Test.cpp:25: undefined reference to `browse'
collect2: error: ld return 1 exit status

file utils.h

#ifndef UTILS_H
#define UTILS_H

#ifdef __cplusplus
extern "C"{
#endif
#pragma once
// several includes..

char * browse(const char * param);
// more functions and variables....

#ifdef __cplusplus
}
#endif
#endif 

file utils.c

#include "utils.h"
char *browse(const char *param){
// do stuff here
}

file Test.cpp

#include "utils.h"

void Test::getTestParams() {
    try{
        string url = _management.getTestUrl();
        char * paramBuf = browse(url.c_str());
        cout << "Params: " << paramBuf << endl;
    } catch(std::exception &e){
        string errorMsg = "getTestParams @Test: error " + string(e.what());
        _textOp.printLog(errorMsg);
        _textOp.writeToLogFile(-1, errorMsg);
    }
}

CMakeLists.txt

cmake_minimum_required (VERSION 3.5)

set (proj_name launcherSpeedtest)
project (${proj_name})

#set(CMAKE_C_FLAGS "-std=c99")
set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror -std=c++11 -pthread")
set (src_dir "${PROJECT_SOURCE_DIR}/src/")

file (GLOB src_files "${src_dir}/*")
file (GLOB pugixml_files "${src_dir}/pugixml-1.9/*.cpp")
file (GLOB base64_files "${src_dir}/base64/*.cpp")

find_package(Boost 1.58 COMPONENTS filesystem regex REQUIRED)
set(CURL_LIBRARY "-lcurl")
find_package(CURL REQUIRED)
if(Boost_FOUND AND CURL_FOUND)
	include_directories(${Boost_INLCUDE_DIRS} ${CURL_INCLUDE_DIR})
	add_executable (${proj_name} ${src_files} ${pugixml_files} ${base64_files})
	target_link_libraries(${proj_name} ${Boost_LIBRARIES} ${CURL_LIBRARIES})
endif()

I've read several threads about similar issues but I could figure it out...
any help is welcome, thanks in advance

[Ganado]

This is partially a guess, but have you tried changing it to

extern "C" {
    #include "utils.h"
}
// ...

in your .cpp file?

[nunorpg]

Yeah, I've already tried that and I ended up with the same result..

[Repeater]

Undefined reference means the linker can't find it. Which means one of the following:

test.c doesn't contain the function (or it's been name-mangled)
test.c isn't being compiled
The compiled test.o object isn't being linked against
The compiled test.o object is being linked in the wrong order

Start by doing the build and link yourself, at the command line, to see if it does actually work. If it does, then you know you've got a cmake problem.