项目的Makefile

Question

I have a Makefile for a project using regex. Thus I need to use g++-4.9 and c++11.

BIN   = bin
OBJ   = src/main.o src/time2.o  src/except.o src/except2.o src/struct.o src/index.o
FLAGS = -lncurses
CC    = g++-4.9  -std=c++11 -Wall -pedantic -Wno-long-long -O0 -ggdb

all: compile

run: compile
    ./$(BIN)

clean:
    rm -f $(BIN) $(OBJ)

compile: $(OBJ)
    $(CC) -o $(BIN) $(OBJ) $(FLAGS)

but when I try to make compile:

 g++ -c -o src/main.o src/main.cpp In file included from /usr/include/c++/4.8/regex:35:0, from src/time2.h:16, from src/main.cpp:3: /usr/include/c++/4.8/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. #error This file requires compiler and library support for the \\ ^ In file included from src/main.cpp:5:0: src/struct.h:99:18: error: 'regex' has not been declared bool isnamegood(regex x,const string& name); ^ 

so I don't understand what is wrong, may you help me please?

Answer 1

The problem is that your compile target already depends on the object files! But they aren't build yet, so make tries to find a rule to build them. Because you have not defined a custom rule, it uses the implicit rule :

Compiling C++ programs no is made automatically from n.cc, n.cpp, or nC with a recipe of the form '$(CXX) $(CPPFLAGS) $(CXXFLAGS) -c'. We encourage you to use the suffix '.cc' for C++ source files instead of '.C'.

This rule will of course not use the flags you set in CC . This explains why the gcc command line printed by make does not match your CC . You can test this by running make with --no-builtin-rules , as this should disable all the implicit rules.

A good idea in such cases is to run make with -d or --debug , I think this should display rule evaluations.

Answer 2

Instead of using the c macros, use the c++ macros

CXX= g++-4.9
CXXFLAGS=  -std=c++11 -Wall -pedantic -Wno-long-long -O0 -ggdb

Then the default rules should pick them up and you need to type less in your makefile.

Also see the complete list of variables (macros) used by Make