C language learning -18-makefile file writing examples and how to generate and call dynamic libraries

One 、 Environmental Science

name	edition
operating system	Red Hat Enterprise Linux Server release 7.9 (Maipo)
CPU	12th Gen Intel Core i7-12700H
Memory	5G
gcc	4.8.5

Two 、 File and directory structure

[[email protected] c_test]# ll
 Total usage  12
drwxr-xr-x 2 root root 4096 6 month   21 15:34 exec
drwxr-xr-x 2 root root   23 6 month   21 14:16 include
drwxr-xr-x 2 root root 4096 4 month    7 15:17 leecode_src
drwxr-xr-x 2 root root   27 6 month   21 15:34 lib
drwxr-xr-x 2 root root   22 6 month   21 15:34 makefile
drwxr-xr-x 2 root root   23 6 month   21 15:34 temp
drwxr-xr-x 2 root root 4096 6 month   21 14:32 test_src

[[email protected] c_test]# ll include/FindMax.h 
-rw-r--r-- 1 root root 90 6 month   21 14:16 include/FindMax.h

[[email protected] c_test]# ll test_src/main.c 
-rw-r--r-- 1 root root 144 6 month   21 14:32 test_src/main.c

[[email protected] c_test]# ll test_src/FindMax.c 
-rw-r--r-- 1 root root 416 6 month   21 14:14 test_src/FindMax.c

3、 ... and 、makefile Implementation content

（1） We need to FindMax.h、FindMax.c Generate binary points O file .
（2） Then according to the binary point O File generation libFindMax.so.
（3） According to libFindMax.so、main.c File generation executable file main.

Why should we have a little O file ？
To speed up compilation efficiency , If it is a big project , Need a lot of points C The composition of the document , It takes a long time to recompile each . If Mr. a little O file , At point C The document has not been changed , No need to recompile the generation point O Of documents , This greatly speeds up compilation time .

Four 、 Source code file

（1）FindMax.h

#ifndef FindMax_H
#define FindMax_H
extern int FindMax(int* Array, int ArraySize);
#endif

It is recommended to add conditional compilation , Avoid repeating statements .

（2）FindMax.c

#include <stdio.h>
#include <FindMax.h>

extern int FindMax(int* Array, int ArraySize);

int main()
{
    
    int Array[] = {
    1,2,3,4,5};
    printf("max : %d\n",FindMax(Array,5));
    return 0;
}

extern int FindMax(int* Array, int ArraySize)
{
    
    int max = Array[0];
    int i;
    
    for(i=1; i<ArraySize; i++)
    {
    
        if(max < Array[i])
        {
    
            max = Array[i];
        }
    }
    return max;
}

In the examples of other people on the Internet, only function definitions and header file references , No addition main Functions and function declarations , I don't know what the hidden trouble is , There are no errors or warnings when compiling , I'm here just for the convenience of my own test , Hee hee .

（3）main.c

#include <stdio.h>
#include <FindMax.h>

int main()
{
    
    int Array[] = {
    1,2,3,4,5};
    printf("max : %d\n",FindMax(Array,5));
    return 0;
}

(4) makefile

CC = gcc
CFLAG_O = -c -Wall -fpic -O3
CFLAG_SO = -shared 
CFLAG_EXEC = -Wall -O3
CFLAG_ALIAS = -o
RM_COMM = rm -rf
SRC_PATH = ../test_src/
EXEC_PATH = ../exec/
TEMP_PATH = ../temp/
INCLUDE_COMMAND = -I
LIB_COMMAND = -L
INCLUDE_PATH = ../include/
LIB_PATH = ../lib/
LIB_NAME = -l

all : main

main : libFindMax.so
	$(CC) $(CFLAG_EXEC) $(CFLAG_ALIAS) $(EXEC_PATH)main $(SRC_PATH)main.c $(INCLUDE_COMMAND) $(INCLUDE_PATH) $(LIB_COMMAND) $(LIB_PATH) $(LIB_NAME)FindMax 

libFindMax.so : FindMax.o
	$(CC) $(CFLAG_SO) $(TEMP_PATH)FindMax.o $(CFLAG_ALIAS) $(LIB_PATH)libFindMax.so 

FindMax.o :
	$(CC) $(CFLAG_O) $(SRC_PATH)FindMax.c $(INCLUDE_COMMAND) $(INCLUDE_PATH) $(CFLAG_ALIAS) $(TEMP_PATH)FindMax.o

clean : 
	$(RM_COMM) $(EXEC_PATH)main $(TEMP_PATH)FindMax.o $(LIB_PATH)libFindMax.so

5、 ... and 、 environment variable

My side libFindMax.so The storage path of the dynamic library is /opt/c_test/lib, Everyone depends on the actual situation , Add this path to /etc/ld.so.conf The last line of the document , In execution /sbin/ldconfig -v Just ok 了

[[email protected] makefile]# cat /etc/ld.so.conf
include ld.so.conf.d/*.conf
/usr/local/openssl/lib
/opt/c_test/lib
[[email protected] makefile]# 
[[email protected] makefile]# 
[[email protected] makefile]# /sbin/ldconfig -v

6、 ... and 、 test result

[[email protected] makefile]# make clean
rm -rf ../exec/main ../temp/FindMax.o ../lib/libFindMax.so
[[email protected] makefile]# 
[[email protected] makefile]# 
[[email protected] makefile]# make
gcc -c -Wall -fpic -O3 ../test_src/FindMax.c -I ../include/ -o ../temp/FindMax.o
gcc -shared  ../temp/FindMax.o -o ../lib/libFindMax.so 
gcc -Wall -O3 -o ../exec/main ../test_src/main.c -I ../include/ -L ../lib/ -lFindMax 
[[email protected] makefile]# 
[[email protected] makefile]# 
[[email protected] makefile]# ../exec/main 
max : 5