Emanuele Vannacci Emanuele Vannacci - 2 months ago 24
C Question

ImageMagic library with Cmake: linking error

I'm programming in C. I want use ImageMagick library but some fuction can't be resolved.

This is my cMakeList.txt file:

cmake_minimum_required(VERSION 3.3)
project(WebServer)

set(CMAKE_C_COMPILER "/usr/bin/gcc")

set(SOURCE_FILES io.c server.c lock_fcntl.c sig_handler.c thread_job.c msg_parser.c)
set(LIB http-parser-master/http_parser.c )

set(CMAKE_USE_PTHREADS_INIT true)
set(CMAKE_USE_PTHREADS_INIT ON)

find_package(Threads REQUIRED)
find_package(ImageMagick COMPONENTS ImageWand)

include_directories(header)
include_directories(http-parser-master)

#include_directories(/usr/local/include/ImageMagick-7/MagickWand)
include_directories(${ImageMagick_INCLUDE_DIRS})

add_executable(server ${SOURCE_FILES} ${LIB})
add_executable(client client.c io.c)
add_executable(main main.c io.c)

target_link_libraries(main ${ImageMagick_LIBRARIES})
target_link_libraries(server Threads::Threads)


and this is the source main.c:

#include <ImageMagick-7/MagickWand/MagickWand.h>
#include "basic.h"

void convert_image(char *path, float quality_factor, char *out) {

int width, height;
MagickWand *n_wand = NULL;

MagickWandGenesis();

m_wand = (struct MagickWand *) NewMagickWand();


MagickReadImage(m_wand,"logo:");

width = MagickGetImageWidth(m_wand);
height = MagickGetImageHeight(m_wand);

if((width /= 2) < 1)width = 1;
if((height /= 2) < 1)height = 1;

MagickResizeImage(m_wand,width,height,LanczosFilter,1);

MagickSetImageCompressionQuality(m_wand,95);

MagickWriteImage(m_wand,"logo_resize.jpg");

if(m_wand)m_wand = (struct MagickWand *) DestroyMagickWand(m_wand);

MagickWandTerminus();
}


On build I get this error:

Scanning dependencies of target main
[ 33%] Building C object CMakeFiles/main.dir/main.c.o
[ 66%] Linking C executable main
CMakeFiles/main.dir/main.c.o: nella funzione "convert_image":
/home/emanuele/ClionProjects/WebServer/main.c:14: riferimento non definito a "MagickWandGenesis"
/home/emanuele/ClionProjects/WebServer/main.c:16: riferimento non definito a "NewMagickWand"
/home/emanuele/ClionProjects/WebServer/main.c:19: riferimento non definito a "MagickReadImage"
/home/emanuele/ClionProjects/WebServer/main.c:22: riferimento non definito a "MagickSetImageCompressionQuality"
/home/emanuele/ClionProjects/WebServer/main.c:25: riferimento non definito a "MagickWriteImage"
/home/emanuele/ClionProjects/WebServer/main.c:28: riferimento non definito a "DestroyMagickWand"
/home/emanuele/ClionProjects/WebServer/main.c:30: riferimento non definito a "MagickWandTerminus"
collect2: error: ld returned 1 exit status
make[3]: *** [main] Errore 1
make[2]: *** [CMakeFiles/main.dir/all] Errore 2
make[1]: *** [CMakeFiles/main.dir/rule] Errore 2
make: *** [main] Errore 2


ImageMagick is correctly installed and it work by command line. How to solve?

Answer

In your case you get the linker errors because find_package cannot find a configuration for the library.

find_package looks for a file in the format of <name>Config.cmake or <lower-case-name>-config.cmake which will set the necessary variables.

Not every library has these files and when not you have to manually specify the library name in target_link_library(...) and other configurations (like library path and include path etc. if necessary)