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Add CMake user input section
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‎CMake/01 CMake - Basics and Scripting.md‎

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# CMake Crash Course - Basics and Scripting
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Author: methylDragon
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Contains a syntax reference for CMake
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Contains a syntax reference for CMake. We'll be going through some concepts, the CLI, and scripting with CMake!
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3.3 [Comments](#3.3)
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3.4 [Printing](#3.4)
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3.5 [Variables](#3.5)
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3.6 [Variable Scope](#3.6)
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3.7 [Cache Variables](#3.7)
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3.8 [Prefixes](#3.8)
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3.9 [Conditionals](#3.9)
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3.10 [Loops](#3.10)
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3.11 [Functions](#3.11)
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3.12 [Macros](#3.12)
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3.6 [Variable Scope and Directories](#3.6)
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3.7 [User Input: Cache Variables](#3.7)
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3.8 [User Input: Options](#3.8)
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3.9 [Prefixes](#3.9)
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3.10 [Conditionals](#3.10)
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3.11 [Loops](#3.11)
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3.12 [Functions](#3.12)
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3.13 [Macros](#3.13)
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cmake -D CMAKE_BUILD_TYPE=Release # This also works!
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```
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> Additionally, do note that this is actually the **best practice for invoking CMake**
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#### **View Cached Variables**
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- CMake requirements
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- Project name
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- Build targets
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- Build **targets**
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> But actually, if you just want to test the basic programming stuff in CMake, you can have an empty `CMakeLists.txt` file with just the statements to test (in most cases!) It won't build anything, but it's good enough.
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>
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set(NUM_LIST 1 2)
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set(EQUIVALENT_NUM_LIST 1;2)
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# You can even append to the lists!
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set(NUM_LIST ${NUM_LIST} 3 4) # So-so way
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list(APPEND NUM_LIST 5 6) # Better way
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# Use variables
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message("WOW_NUM: ${WOW_NUM}")
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message("EQUIVALENT_NUM_LIST: ${EQUIVALENT_NUM_LIST}")
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### 3.6 Variable Scope <a name="3.6"></a>
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### 3.6 Variable Scope and Directories <a name="3.6"></a>
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[go to top](#top)
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![img](assets/cmake-variable-scopes.png)
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[Image Source](<https://preshing.com/20170522/learn-cmakes-scripting-language-in-15-minutes/>)
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Variables are created in the scope they are set in. And scopes are defined by directories and functions. So just think of C++ scopes, and you should be fine.
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Variables are created in the scope they are set in. And scopes are defined by directories and functions.
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> **Directories!?**
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>
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> Yes! Directories! Since each `CMakeLists.txt` file governs its directory, so treat them modularly like that
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So just think of C++ scopes, and you should be fine.
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Luckily, there is a way to state that a variable is set in its parent scope, instead of its current scope.
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### 3.7 Cache Variables <a name="3.7"></a>
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### 3.7 User Input: Cache Variables <a name="3.7"></a>
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[go to top](#top)
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CMake uses a cache, which is really just a text file called `CMakeCache.txt` to remember settings so you don't have to restate them when running CMake.
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Normal variables aren't placed in the cache unless you explicitly tell CMake to though! **Adding a variable as a cache variable also exposes them in the command line**.
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Normal variables aren't placed in the cache unless you explicitly tell CMake to though! **Adding a variable as a cache variable also exposes them in the command line**. If you don't set them in the command line, they'll use their default value, so it's a good way to create **settable variables with default values**!
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#### **Listing Cache Variables**
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You can list out all the available settable cache variables from the command line!
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Just use these commands:
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```shell
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cmake -L # List all non-advanced cache variables
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cmake -LA # List all cache varialbes (including advanced ones)
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cmake -LAH # List all cache variables, and also display help for them
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```
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#### **Setting Cache Variables in the Command Line**
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Same as setting variables in the command line.
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```shell
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cmake -DCACHE_VAR_NAME=rawr
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# Or with type hints
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cmake -DTYPED_CACHE_VAR_NAME:STRING=raa
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```
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#### **Setting Cache Variables**
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```cmake
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# General call
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### 3.8 Prefixes <a name="3.8"></a>
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### 3.8 User Input: Options <a name="3.8"></a>
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[go to top](#top)
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These are just boolean cache variables that you can set ON or OFF in the command line.
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#### **Listing Options**
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If you want to use options, you can use the same cache variable interface.
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> You can list out all the available settable cache variables from the command line!
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>
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> Just use these commands:
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>
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> ```shell
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> cmake -L # List all non-advanced cache variables
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> cmake -LA # List all cache varialbes (including advanced ones)
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> cmake -LAH # List all cache variables, and also display help for them
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> ```
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#### **Setting Options in the Command Line**
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Same as setting variables in the command line.
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```shell
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cmake -DOPTION_NAME=ON
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```
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#### **Setting Options**
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```cmake
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option(OPTION_NAME "SOME_RANDOM_DOCSTRINGS" ON) # OPTION_NAME is default ON
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# You can also set a dependent option!
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# This one defaults to ON
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# If and only if ON_ME_BEING_ON is ON and AND_ON_ME_BEING_OFF is OFF
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CMAKE_DEPENDENT_OPTION(DEP_OPTION "I'm dependent!!" ON
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"ON_ME_BEING_ON;NOT AND_ON_ME_BEING_OFF" OFF)
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```
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### 3.9 Prefixes <a name="3.9"></a>
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[go to top](#top)
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### 3.9 Conditionals <a name="3.9"></a>
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### 3.10 Conditionals <a name="3.10"></a>
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endif()
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```
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Cool! You can control program flow depending on whether stuff evaluates `TRUE` or `FALSE`
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Cool! You can control program flow depending on whether stuff evaluates `TRUE` or `FALSE`.
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#### **Boolean Constants**
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`IGNORE`, `NOTFOUND`, an empty string, or strings that end with the suffix "-NOTFOUND"
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#### **Example Usage**
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```cmake
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> The `if()` statement is a little weird in this regard, because it takes in both variables and constants! In this case, if we wrapped VAR and passed it in as `if(${VAR})`, the if statement evaluates it as the string "TRUE" as opposed to the boolean constant `TRUE`.
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#### **Logic**
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You can do logic with the expressions that go into `if()`!
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### 3.10 Loops <a name="3.10"></a>
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### 3.11 Loops <a name="3.11"></a>
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endforeach()
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```
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#### **For Loop over a Range**
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![1565773727787](assets/1565773727787.png)
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endforeach()
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```
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#### **While Loop**
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The while loop conditions are resolved in the same way the `if()` command resolves conditions.
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### 3.11 Functions <a name="3.11"></a>
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### 3.12 Functions <a name="3.12"></a>
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### 3.12 Macros <a name="3.12"></a>
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### 3.13 Macros <a name="3.13"></a>
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[go to top](#top)
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