How to include -std=c++11 and -lpthread in makefile?

Question

I tried the advice in this answer, but it's for GCC and didn't help anyways.

I want to #include <thread> in a file, so I have a make file as the following:

OBJS    = clitest.o Sources/NClient.o
CC      = g++
DEBUG   = -g
CFLAGS  = -Wall -c $(DEBUG)
LFLAGS  = -Wall $(DEBUG)

clitest: $(OBJS)
    $(CC) $(LFLAGS) $(OBJS) -o clitest

Where should I include -std=c++11 and -lpthread in this? I've tried just about every combination I can, but I continue to get this error when I run make:

/usr/include/c++/4.8.3/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support is currently experimental, and must be enabled with the -std=c++11 or -std=gnu++11 compiler options.

I believe this is the command it's running?

[jaska@localhost NClient]make
g++    -c -o clitest.o clitest.cpp

Here's the source code file, too:

#include <thread>
#include <string>

void task(std::string msg){
    std::cout << msg << '\n';
}

...
...

std::thread t1(task, "message");
client->create();
t1.join();

Answer 1

Your makefile doesn't have an explicit rule for compiling the objects in $(OBJS) so that means the implicit rule will be used, which is what produces this command:

g++    -c -o clitest.o clitest.cpp

The implicit rule for turning a .cpp file into a .o file is approximately:

$(CXX) $(CXXFLAGS) -c -o $@ $<

so to add options that affect that rule you should add them to the CXXFLAGS variable (CFLAGS is conventionally used for compiling C files, and CC is the C compiler, the conventional variable for the C++ compiler is CXX).

The -lpthread option is a linker option, so need to be given during linking. You have defined your own rule for linking, so you should either add -lpthread to that recipe or add it to the LFLAGS variable.

N.B. using -Wall and -g during linking is useless, they have no effect.

N.B. adding -c to the CFLAGS is wrong, the implicit rules for compiling .c files already include -c, just as the implicit one for C++ files includes -c. This doesn't cause any problems because the CFLAGS variable is not used by your makefile, or by the implicit rule for compiling .cpp files.

N.B. instead of linking to -lpthread you should compile and link with -pthread

N.B. the implicit rule for linking, and makefile convention, is to use the variable LDFLAGS for linker options, and LIBS for libraries such as -lpthread, so I would rewrite your makefile as:

OBJS    = clitest.o Sources/NClient.o
CXX     = g++
DEBUG   = -g
CXXFLAGS  = -Wall $(DEBUG) -std=c++11 -pthread
LDFLAGS = -pthread

clitest: $(OBJS)
    $(CXX) $(LDFLAGS) -o $@ $^ $(LIBS)

This still relies on the implicit rule for turning the .cpp files into .o files, but now that implicit rule will pick up the right options from the CXXFLAGS variable.