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

Solution 1

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)

Solution 2

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

1. To download zlib, if on Linux with

    sudo apt-get install zlib1g-dev
   

   and then following what Matthieu proprosed.

2. Or download zlib like in 1 and do:

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

3. 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})
    target_link_libraries(my_executable zlib)
   

Comments

[Felix Xu]

sudo apt-get install zlib1g-dev should be highlighted, it's important.

[Dotl]

In 3., where is ZLIB_DEPS defined?

[AKJ]

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.

[WhozCraig]

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) ?

[AKJ]

@WhozCraig you are right. I made a mistake. ZLIB_DEPS and ZLIB_DEPS_DIR should be the same variables.