Passing an argument to CMAKE via command prompt

Question

I have a makefile for my project, with which I can pass an argument that controls certain build flags. Now I want to do the same using CMake. I have created CMakeLists.txt but I don't know how to pass the argument and check for the argument value in CMakeLists.txt.

Sample of my Makefile:

ifeq "$(MY_VARIABLE)" "option_value" //setting some flags else //setting some other flag endif

I then call make using make MY_VARIABLE=option_value. What is the way in CMake to take the argument from command prompt and set flags based on that?

Peter · Accepted Answer · 2022-10-05 12:22:18Z

103

In the CMakeLists.txt file, create a cache variable, as documented here:

SET(MY_VARIABLE "option_value" CACHE STRING "Some user-specified option")

Source: https://cmake.org/cmake/help/latest/command/set.html#set-cache-entry

Then, either use the GUI (ccmake or cmake-gui) to set the cache variable, or specify the value of the variable on the cmake command line with -D:

cmake -DMY_VARIABLE:STRING=option_value2

Modify your cache variable to a boolean if, in fact, your option is boolean.

edited Oct 5, 2022 at 12:22

answered Oct 15, 2012 at 15:33

Peter

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4 Comments

user997112 Over a year ago

If you create the cache variable in the CMakeLists.txt file and then pass the argument via calling cmake, won't the CMakeList.txt file keep overwriting the argument value?

Peter Over a year ago

No, the cache is populated on the first run with either the default value, or the value supplied on the command line if it is provided. After the first run, the CMakeLists.txt SET command is ignored and the cache value is used. This allows you to adjust these options and have them persist.

user997112 Over a year ago

I created a boolean putting SET() in my CMakeList.txt with "false" and then I called the cmake command, with "true". From my experiment the value in SET() sees to be the default?

Peter Over a year ago

Whatever is in SET is the default, meaning if not specified on the command line. Command line always overrides, even if cache is already set. If you still have questions please ask a new question

PJ_Finnegan · Accepted Answer · 2019-04-19 08:42:03Z

CMake 3.13 on Ubuntu 16.04

This approach is more flexible because it doesn't constraint MY_VARIABLE to a type:

$ cat CMakeLists.txt message("MY_VARIABLE=${MY_VARIABLE}") if( MY_VARIABLE ) message("MY_VARIABLE evaluates to True") endif() $ mkdir build && cd build $ cmake .. MY_VARIABLE= -- Configuring done -- Generating done -- Build files have been written to: /path/to/build $ cmake .. -DMY_VARIABLE=True MY_VARIABLE=True MY_VARIABLE evaluates to True -- Configuring done -- Generating done -- Build files have been written to: /path/to/build $ cmake .. -DMY_VARIABLE=False MY_VARIABLE=False -- Configuring done -- Generating done -- Build files have been written to: /path/to/build $ cmake .. -DMY_VARIABLE=1 MY_VARIABLE=1 MY_VARIABLE evaluates to True -- Configuring done -- Generating done -- Build files have been written to: /path/to/build $ cmake .. -DMY_VARIABLE=0 MY_VARIABLE=0 -- Configuring done -- Generating done -- Build files have been written to: /path/to/build

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