[Linux] makefile multi-directory

Before writing the use of multi-directory makefile need to have several functions and symbols

Custom Variables

target=edit
When referenced directly$(target)

A bit like the C language #define, here $(target)will be replaced edit.

You can also replace multiple files, pay attention to space

object=main.o xxx.o xxx.o

Automatic variables

Automatic variables are used in the second row is gcc -c xxxin

$<: The first rule of a dependent
$@: Target rule
$^: Rule all depends

$(target):$(obj)
gcc \$^ -o \$@

This line means that the rules all the dependencies ($ ^) (. O files) to generate the target ($ @)

$(target)

Auto match

Sub rule:
目标：依赖

%.o:%.c
Rely on automatic matching of the ultimate goal:
main.o: main.c
add.o: add.c
sub.o: sub.c

makefile function

pro=$(wildcard src/*.c)
src=$(wildcard *.c)
obj=$(patsubst %.c,%.o,$(pro) $(src))

wildcardFind all .c files in the current directory and the src directory, and are returned to the pro src
pro=$(wildcard *.c)
src=$(wildcard src/*.c)
patsubstreplace all .c files to .o files
obj=$(patsubst %.c,%.o,$(pro) $(src))

Note:
I will be here with a space $(pro) $(src)separated, so at compile time system is not main.cxxx.cthe case, that is connected to the head and tail.

So, preparatory work is complete.

Code

.
├── main.c
├── makefile
└── src
    ├── Speak.c
    └── Speak.h

main.c

#include <stdio.h>
#include "src/Speak.h"
int main()
{
    printf("Helo\n");
    Speak();
    return 0;
}

src/Speak.c

#include "Speak.h"

void Speak(void)
{
printf("Speak\n");
}

src/Speak.h

#include <stdio.h>
void Speak(void);

---

Here began to explain the makefile

pro=$(wildcard *.c)
src=$(wildcard src/*.c)
obj=$(patsubst %.c,%.o,$(pro) $(src))

target=edit

$(target):$(obj)
    gcc $^ -o $@
%.o:%.c
    gcc -c $< -o $@

.PHONY:clean
clean:
    rm  $(obj) $(target) -f

We will root .c files in the directory (only one main.c) through a wildcardreturn to thepro

src.C files in the directory by wildcardthe return tosrc

By patsubstreplacing all .c files to .o files

By then rely on automatic matching

%.o:%.c
    gcc -c $< -o $@

.O files are generated every .c file

The final edit is generated executable file

$(target):$(obj)
    gcc $^ -o $@

sort out:

1. Using the wildcardreturn .c files in each directory,

2. The use of patsubstindividual .c into .o (This step does not generate .o file, only the equivalent of a main.creturn to main.o)

3. The use of automatic matching to automatically generate various .o (this step is to generate .o file)

4. All .o executable file edit