Define macros in makefile and pass them to source code

makefile yes liunx Under the platform c、c++ Develop indispensable tools , Master some makefile The skills of are very helpful for project compilation and construction , This article mainly records makefile Macro definition and pass it to the source code , It mainly conveys a code_version Variable , Variables are passed through git Command acquisition commit id, Pass the macro definition to the source code , In the source code, you can get commit id, It can be used as code Version information for , This is for frequent release The project is very important , Can confirm some so Does the version of match .

1 Project directory structure

The establishment of a demo The structure of the project catalogue is as follows ：

├── include
│   └── common.h
├── main_dir
│   ├── main.c
│   └── makefile
├── makefile
├── obj
│   ├── function.o
│   └── main.o
├── readme.txt
└── sub_dir
    ├── function.c
    └── makefile

2 Top level directory makefile Reading

Top level directory makefile：

CC = gcc
CFLAGS = -g -Wall -O 
export TARGET = demo

export OBJ = function.o main.o
export BUILD_PATH = $(PWD)
export SUBDIR = main_dir sub_dir
export OBJDIR = $(BUILD_PATH)

export code_version = $(shell (git rev-parse --short HEAD))
export code_branch = $(shell (git branch))
export code_date= $(shell (git log -1 --format=%cd ))

$(info $(code_version))
$(info $(code_branch))
$(info $(code_date))

all:sub_target $(TARGET)

$(TARGET):$(OBJ) 
	$(CC) $^ -o $(OBJDIR)/[email protected] 
	@echo "-------build target success-------"

sub_target:
	@echo "-------start build sub dir-------"
	make -C main_dir
	make -C sub_dir
	@echo "-------build sub dir end-------"

clean:
	rm -rf $(OBJDIR)/*.o $(TARGET) 

top floor makefile The goal is to compile demo Executable program , compile demo Need to rely on main_dir and sub_dir Compile the function.o and main.o, And compile function.o and main.o Store it in obj Folder , This is convenient for project management . The top-level directory also passes shell The command defines code_version Variable , In this way, others in the project makefile You can use this variable , This is also makefile A way to pass variables between .

2 main_dir Directory source code interpretation

main_dir There is a main.c And a makefile file ,main.c Enter the following contents ：

#include <stdio.h>
#include "../include/common.h"

int main()
{
    
    printf("code version: %s\n", CODE_VERSION);
    printf("main IN\n");

    int sum = add(5, 6);
    printf("sum = %d \n",sum);

    printf("main OUT\n");
    return 0;
}

It mainly calls a add function ,add The declaration of the function is in include/common.h, Realize in sub_dir/function.c,common.h The content in is very simple , Only do the add Function declaration ：

int add (int a, int b);

main Function also prints CODE_VERSION This macro , The macro in common.h and main.c There is no definition in , It passes when compiling makefile Defined ,main_dir in makefile Content into the next ：

CFLAGS += -DCODE_VERSION=\"$(code_version)\"

$(OBJDIR)/main.o:main.c
	$(CC) $(CFLAGS) -c $^ -o [email protected]

among ：

CFLAGS += -DCODE_VERSION=\"$(code_version)\"

That's the definition CODE_VERSION This macro , And the content of the macro is the top level makefile Variables passed in , Besides ,makefile You need to use escape characters when defining string macros in .

3 sub_dir Directory source code interpretation

sub_dir The directory contains a function.c Documents and a makefile,function.c The middle is add Function implementation ：

#include <stdio.h>
#include "../include/common.h"

int add (int a, int b)
{
    
    return a+b;
}

sub_dir in makefile Content ：

$(OBJDIR)/function.o:function.c
	$(CC) $(CFLAGS) -c $^ -o [email protected]

4 Effect validation

Execute in the top-level directory make Command to compile :

make

The compilation results are as follows ：

Run the program ：

./demo

give the result as follows ：

You can see CODE_VERSION Some are printed correctly .
Experimental code git Address ：https://github.com/zhenghaiyang123/makefile_demo.git