General engineering

New Project-> C Project

mysharedlibrary

/*
 * libMysharedlibrary.h
 *
 *  Created on: 2023年8月23日
 *      Author: yeqiang
 */

#ifndef LIBMYSHAREDLIBRARY_H_
#define LIBMYSHAREDLIBRARY_H_

extern void mysharedlibraryfunc ();

#endif /* LIBMYSHAREDLIBRARY_H_ */

/*
 * mysharedlibrary.c
 *
 *  Created on: 2023年8月23日
 *      Author: yeqiang
 */

#include <stdio.h>
#include "libMysharedlibrary.h"

void mysharedlibraryfunc (){
	printf("mysharedlibrary func...\n");
}

build

13:33:10 **** Build of configuration Debug for project mysharedlibrary ****
make all 
Building file: ../mysharedlibrary.c
Invoking: GCC C Compiler
gcc -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"mysharedlibrary.d" -MT"mysharedlibrary.o" -o "mysharedlibrary.o" "../mysharedlibrary.c"
Finished building: ../mysharedlibrary.c
 
Building target: libmysharedlibrary.so
Invoking: GCC C Linker
gcc -shared -o "libmysharedlibrary.so" ./mysharedlibrary.o   
Finished building target: libmysharedlibrary.so
 

13:33:11 Build Finished. 0 errors, 0 warnings. (took 165ms)

New Project-> C Project

configure include

configure the library

source code

/*
 ============================================================================
 Name        : executableproj.c
 Author      : 
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>
#include "libMysharedlibrary.h"

int main(void) {
	puts("Hello World"); /* prints Hello World */
	mysharedlibraryfunc();
	return EXIT_SUCCESS;
}

build

13:36:50 **** Build of configuration Debug for project executableproj ****
make all 
Building file: ../src/executableproj.c
Invoking: GCC C Compiler
gcc -I/home/yeqiang/eclipse-workspace/mysharedlibrary -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/executableproj.d" -MT"src/executableproj.o" -o "src/executableproj.o" "../src/executableproj.c"
Finished building: ../src/executableproj.c
 
Building target: executableproj
Invoking: GCC C Linker
gcc -L/home/yeqiang/eclipse-workspace/mysharedlibrary/Debug -o "executableproj" ./src/executableproj.o   -lmysharedlibrary
Finished building target: executableproj
 

13:36:50 Build Finished. 0 errors, 0 warnings. (took 166ms)

Execution, error: cannot open shared object file: No such file or directory

Reason: The libmysharedlibrary.so directory is not configured to /etc/ld.so.conf

Define the environment variable LD_LIBRARY_PATH at zero time and succeed.

Gnu AutoTools project

Makefile.am

bin_PROGRAMS=a.out
a_out_SOURCES=test.c

# Linker options for a.out
a_out_LDFLAGS = -L/home/yeqiang/eclipse-workspace/mysharedlibrary/Debug -lmysharedlibrary

# Compiler options for a.out
a_out_CPPFLAGS = -I/home/yeqiang/eclipse-workspace/mysharedlibrary

build 报错 undefined reference to `mysharedlibraryfunc'

13:43:16 **** Build of configuration Build (GNU) for project test ****
make all 
Making all in src
make[1]: 进入目录“/home/yeqiang/eclipse-workspace/test/src”
gcc -DPACKAGE_NAME=\"test\" -DPACKAGE_TARNAME=\"test\" -DPACKAGE_VERSION=\"1.0\" -DPACKAGE_STRING=\"test\ 1.0\" -DPACKAGE_BUGREPORT=\"\" -DPACKAGE_URL=\"\" -DPACKAGE=\"test\" -DVERSION=\"1.0\" -I.  -I/home/yeqiang/eclipse-workspace/mysharedlibrary   -g -O2 -MT a_out-test.o -MD -MP -MF .deps/a_out-test.Tpo -c -o a_out-test.o `test -f 'test.c' || echo './'`test.c
mv -f .deps/a_out-test.Tpo .deps/a_out-test.Po
gcc  -g -O2 -L/home/yeqiang/eclipse-workspace/mysharedlibrary/Debug -lmysharedlibrary  -o a.out a_out-test.o  
/usr/bin/ld: a_out-test.o: in function `main':
/home/yeqiang/eclipse-workspace/test/src/test.c:17: undefined reference to `mysharedlibraryfunc'
collect2: error: ld returned 1 exit status
make[1]: *** [Makefile:353：a.out] 错误 1
make[1]: 离开目录“/home/yeqiang/eclipse-workspace/test/src”
make: *** [Makefile:348：all-recursive] 错误 1
"make all" terminated with exit code 2. Build might be incomplete.

13:43:16 Build Failed. 4 errors, 0 warnings. (took 166ms)

After testing, the most basic dynamic library linking process

gcc -I/home/yeqiang/eclipse-workspace/mysharedlibrary  -c -o "executableproj.o" "executableproj.c"
gcc -L/home/yeqiang/eclipse-workspace/mysharedlibrary/Debug -o "executableproj" executableproj.o   -lmysharedlibrary

Can be executed successfully

After repeated testing, it was found that the successful operation process of manual execution is as follows

gcc -I/home/yeqiang/eclipse-workspace/mysharedlibrary  -c -o a_out-test.o test.c
gcc -L/home/yeqiang/eclipse-workspace/mysharedlibrary/Debug -o a.out a_out-test.o -lmysharedlibrary

The failure process is as follows

gcc -I/home/yeqiang/eclipse-workspace/mysharedlibrary  -c -o a_out-test.o test.c
gcc -L/home/yeqiang/eclipse-workspace/mysharedlibrary/Debug -lmysharedlibrary  -o a.out a_out-test.o

That is: the root cause of undefined reference to `mysharedlibraryfunc' caused by Gnu Autotools Project linking dynamic library is that the -l parameter (-lmysharedlibrary) should be followed by the gcc command, not before the a_out-test.o parameter!

Makefile.in is automatically generated, and it will be overwritten every time it is compiled. It is impossible to modify the parameter position here, gcc bug?

After further analysis, it was found that clang 16 does not have this problem, is it a gcc bug?

Finally solved, using clang to compile

Modify src/Makefile.am, define the CC variable, and point to clang

bin_PROGRAMS=a.out
a_out_SOURCES=test.c

CC=/usr/local/bin/clang
# Linker options for a.out
AM_LDFLAGS = -L/home/yeqiang/eclipse-workspace/mysharedlibrary/Debug -lmysharedlibrary

# Compiler options for a.out
AM_CPPFLAGS = -I/home/yeqiang/eclipse-workspace/mysharedlibrary

compile

14:53:40 **** Build of configuration Build (GNU) for project test ****
make all 
Making all in src
make[1]: 进入目录“/home/yeqiang/eclipse-workspace/test/src”
/usr/local/bin/clang -DPACKAGE_NAME=\"test\" -DPACKAGE_TARNAME=\"test\" -DPACKAGE_VERSION=\"1.0\" -DPACKAGE_STRING=\"test\ 1.0\" -DPACKAGE_BUGREPORT=\"\" -DPACKAGE_URL=\"\" -DPACKAGE=\"test\" -DVERSION=\"1.0\" -I.  -I/home/yeqiang/eclipse-workspace/mysharedlibrary   -g -O2 -MT test.o -MD -MP -MF .deps/test.Tpo -c -o test.o test.c
mv -f .deps/test.Tpo .deps/test.Po
/usr/local/bin/clang  -g -O2 -L/home/yeqiang/eclipse-workspace/mysharedlibrary/Debug -lmysharedlibrary  -o a.out test.o  
make[1]: 离开目录“/home/yeqiang/eclipse-workspace/test/src”
make[1]: 进入目录“/home/yeqiang/eclipse-workspace/test”
make[1]: 对“all-am”无需做任何事。
make[1]: 离开目录“/home/yeqiang/eclipse-workspace/test”

14:53:40 Build Finished. 0 errors, 0 warnings. (took 265ms)

run

linux c shared library dynamic link library development call notes common project gnu autotools project error undefined reference

General engineering

Gnu AutoTools project

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