Building of executable and shared library with cmake, runtimelinker does not find dll

Question

I am working with gcc(cygwin), gnu make, windows 7 and cmake.

my cmake testprojekt has the following structure

rootdir
|-- App
|   |-- app.cpp
|   +-- CMakeLists.txt
|-- Lib
|   |-- lib.cpp
|   |-- CMakeLists.txt
|-- MakeFileProject
+ CMakeLists.txt

rootdir/App/app.cpp:

#include<string>
void printThemMessageToScreen(std::string input);//prototype
int main(int argc,char **argv){
 printThemMessageToScreen("this will be displayed by our lib");
 return 0;
}

rootdir/Lib/lib.cpp:

#include<iostream>
#include<string>

void printThemMessageToScreen(std::string input){
 std::cout<<input;
}

rootdir/CMakeLists.txt:

cmake_minimum_required(VERSION 2.6)
project(TestProject)

add_subdirectory(App)
add_subdirectory(Lib)

rootdir/Lib/CMakeLists.txt:

add_library(Lib SHARED lib.cpp)

rootdir/App/CMakeLists.txt:

# Make sure the compiler can find include files from our Lib library. 
include_directories (${LIB_SOURCE_DIR}/Lib) 

# Make sure the linker can find the Lib library once it is built. 
link_directories (${LIB_BINARY_DIR}/Lib) 

# Add executable called "TestProjectExecutable" that is built from the source files 
add_executable (TestProjectExecutable app.cpp) 

# Link the executable to the lib library. 
target_link_libraries (TestProjectExecutable Lib) 

Now, when i run cmake and make, everything will get generated & built with no errors, but when i try to execute the binary, it will fail because the library which was generated could not be found.

BUT: when i copy the lib dll into the same directory like the app exe, it will get executed!

also: if i configure the library to be static, it will also execute.

how to tell the runtime linker where to look for my dll?

UPDATE:

Solution according to the Method proposed by User Vorren:

I opened up the registry editor, and navigated to the following Key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths

, here i created a new key with the name of my Applikation:

in this case : TestProjectExecutable.exe

after that, the (default) value was set to the full path of TestProjectExecutable.exe including the filename and extension. Then i created another String Value called "Path" and set the value to the folder where the dll was located:

Answer 1

Your problem lies not with linker or compiler, but with the way Windows searches for DLL's.

The OS will use the following algorithm to locate the required DLL's:

Look in:

1. The directories listed in the Application-specific Path registry key;
2. The directory where the executable module for the current process is located;
3. The current directory;
4. The Windows system directory;
5. The Windows directory;
6. The directories listed in the PATH environment variable;

Thus you have two reasonable options if you don't want to clutter the OS directories with your app-specific dll:

1. Create an app-specific Path registry entry (I would go with this option);
2. Put your DLL in the same folder as your EXE;
3. Modify the PATH variable (but why would you do that, if you can go with option 1?);

Answer 2

A solution I prefer that hasn't really been mentioned, is build your shared-libs into the same directory as your executables. This tends to be a much simpler solution.

One way to do this with cmake is

set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)

Or you can also set output directories based on build flavours.

See how do I make cmake output into a 'bin' dir?