How to link Zlib with Cmake

Question

I am trying to link my file with the zlib libray but still get: undefined reference to `deflateInit_'.

I am currently using CLion, have downloaded the zLib file from the homepage and added it into the project. This is how my CmakeLists.txt looks like

cmake_minimum_required(VERSION 3.10) project(GzipTest)

set(CMAKE_CXX_STANDARD 11)

include_directories(ZLIB zlib-1.2.11)

add_executable(GzipTest main.cpp zlib-1.2.11/zlib.h)

And the code (Copying from the zpipe.c):

include "iostream"

include "zlib.h"

include "iostream"

define CHUNK 1639


FILE *fp;


int def(FILE *source, FILE *dest, int level){
    int ret, flush;
    unsigned have;
    z_stream strm;
    unsigned char in[CHUNK];
    unsigned char out[CHUNK];

    // Allocate Deflate state
    strm.zalloc = Z_NULL;
    strm.zfree = Z_NULL;
    strm.opaque = Z_NULL;

    ret = deflateInit(&strm, level);
    if (ret != Z_OK){
        return ret;
    }

}


int main(){
    fp = fopen("inputFile.txt", "r");
    if (fp == nullptr){
        perror("Could not open data");
        exit(EXIT_FAILURE);
    }
    def(fp, fp, 1); 
}

What could be missing? Thanks in advance

You don't build with the zlib source file, or link with the zlib library. — Some programmer dude, Nov 14 '18 at 10:56
You have doanloaded a package, there is a README in it with the instructions on how to build it on all platforms. You can also directly get a prebuilt package. — Matthieu Brucher, Nov 14 '18 at 10:59
Matthieu, the readme: # To install libz.a, zconf.h and zlib.h in the system directories, type: # # make install -fwin32/Makefile.gcc. — AKJ, Nov 14 '18 at 11:23

score 22 · Answer 1 · edited Mar 06 '20 at 23:52

22

You have to link against zlib.

If you used:

find_package(ZLIB)

Then you should have:

target_link_libraries(GzipTest ZLIB::ZLIB)

Also don't add the headers to your source files:

add_executable(GzipTest main.cpp)

edited Mar 06 '20 at 23:52

Richard

56,349
34
180
251

answered Nov 14 '18 at 10:56

Matthieu Brucher

21,634
7
38
62

1

Should i replace ${ZLIB_LIBRARIES} with something? I get : CMake Error at CMakeLists.txt:9 (target_link_library): Unknown CMake command "target_link_library". – AKJ Nov 14 '18 at 10:59
That's assuming that you have the package built, and that you are setting the paths to find zlib for cmake properly. And yes, fixed a type, should be librarIES, not librarY. – Matthieu Brucher Nov 14 '18 at 11:00
@AKJ which version of cmake are you using? – Philipp Nov 14 '18 at 11:01
I am really a noob at this. Can you please instruct me on what to do? – AKJ Nov 14 '18 at 11:02
in the cmake-gui (or ccmake on Linux, but in that case, you should already have a zlib package with the system), you need to fill the path to zlib as the errors that find_package indicates. – Matthieu Brucher Nov 14 '18 at 11:04
Philipp, i am using Cmake 3.10.2 – AKJ Nov 14 '18 at 11:17
@AKJ You need to use `target_link_libraries`, not `target_link_library` (note the plural form). – Michael Schlottke-Lakemper Jul 30 '19 at 06:33
@Michael, i have already solved the issue. It is easier once one has mastered CMake. – AKJ Aug 01 '19 at 04:19

score 7 · Answer 2 · edited Sep 28 '22 at 09:42

7

It seems this old post is getting a lot of traction. The solutions to linking zlib with CMake are either:

To download zlib, if on Linux with
```
 sudo apt-get install zlib1g-dev
```
and then following what Matthieu proprosed.

Or download zlib like in 1 and do:

 add_executable(my_executable main.cpp)
 target_link_libraries(my_executable z)

Or just download zlib from their homepage: https://zlib.net/, then save it in a 'deps' folder. Modify the CMakeList in the zlib folder with

 set(ZLIB_DEPS_DIR ${CMAKE_CURRENT_BINARY_DIR} PARENT_SCOPE)

and in the main CMakeList, do

 add_executable(my_executable main.cpp)
 add_subdirectory(deps)
 include_directories(my_executable ${ZLIB_DEPS_DIR})
 target_link_libraries(my_executable zlib)

edited Sep 28 '22 at 09:42

umläute

28,885
9
68
122

answered Jul 04 '19 at 11:18

AKJ

950
2
13
18

`sudo apt-get install zlib1g-dev` should be highlighted, it's important. – Nov 02 '19 at 01:32
In `3.`, where is `ZLIB_DEPS` defined? – Dotl May 02 '20 at 21:41
`ZLIB_DEPS` is not defined anywhere. It is being assigned. Like x = 2, where x is the `ZLIB_DEPS_DIR` and CMAKE_CURRENT_BINARY_DIR is 2. – AKJ May 07 '20 at 16:01
I understand, but that wasn't the question. The actual ZLIB_DEPS variable in the above is never set, and assumed to be an artifact of the subdirectory addition? The question wasn't about ZLIB_DEPS_DIR ; it was about ZLIB_DEPS. Or is the latter just wrong and it was *supposed* to be ZLIB_DEPS_DIR in *all* occurrences in (3) ? – WhozCraig Jan 20 '22 at 10:31
@WhozCraig you are right. I made a mistake. ZLIB_DEPS and ZLIB_DEPS_DIR should be the same variables. – AKJ Jan 21 '22 at 11:01

How to link Zlib with Cmake

2 Answers2

Linked