C 程序链接错误：未定义对“jpeg_std_error”的引用

Question

I use the libjpeg in my C program, and some error occurrs when the program compiled:

/usr/bin/ld: CMakeFiles/video_capture.dir/main.c.o: in function `setup_jpeg_decompress':
/home/arthurryan/programs/video_capture/main.c:58: undefined reference to `jpeg_std_error'
/usr/bin/ld: /home/arthurryan/programs/video_capture/main.c:59: undefined reference to `jpeg_CreateDecompress'
collect2: error: ld returned 1 exit status

I have tried some solutions like:

1. add -ljpeg
2. add -l:<libjpeg.so file path>

But nothing worked. I'm sure that the libjpeg has benn installed in my computer. When I execute

find /usr -iname libjpeg\*so\*

There are several results:

/usr/lib/x86_64-linux-gnu/libjpeg.so.8.2.2
/usr/lib/x86_64-linux-gnu/libjpeg.so
/usr/lib/x86_64-linux-gnu/libjpeg.so.8

If there are any other ways to solve the problem?

I use CLion to develop, here is the content of CMakeLists.txt

cmake_minimum_required(VERSION 3.17)
project(video_capture C)

set(CMAKE_C_STANDARD 11)

set(CMAKE_C_FLAGS -g)
set(CMAKE_C_FLAGS "-L /usr/lib/x86_64-linux-gnu")
set(CMAKE_C_FLAGS "-ljpeg")
set(CMAKE_C_FLAGS "-pthread")

add_executable(video_capture main.c camera/camera.c inc/camera.h inc/common.h camera/logi_c270.c inc/logi_c270.h encoder.c inc/encoder.h converter/jpeg2yuv.c inc/jpeg2yuv.h)
include_directories(./inc)

Answer 1

The way gcc/g++ search libraries changed a while ago. It used not to matter whether your makefile had:

gcc -o stuff -ljpeg stuff.o

or

gcc -o stuff stuff.o -ljpeg

but now, it does matter. The first one won't pick up the needed functions. The second one will.