Utilizing CMAKE_CURRENT_SOURCE_DIR for Efficient File Path Management

What is CMAKE_CURRENT_SOURCE_DIR?

In CMake, CMAKE_CURRENT_SOURCE_DIR is a built-in variable that represents the absolute path to the source directory currently being processed. This variable is particularly useful when you need to reference files or resources that are located relative to the current CMakeLists.txt file.

Key Points

• CMakeLists.txt Scope
  The directory referenced by CMAKE_CURRENT_SOURCE_DIR is determined by the closest CMakeLists.txt file in the source tree hierarchy. Subdirectories can have their own CMAKE_CURRENT_SOURCE_DIR values.
• Full Path
  It always provides the complete path, including the drive letter (on Windows) or mount point (on Unix-like systems).
• Dynamic Value
  The value of CMAKE_CURRENT_SOURCE_DIR changes as CMake processes different source directories within your project.

Common Use Cases

• Generating Code
  You can employ CMAKE_CURRENT_SOURCE_DIR to dynamically generate code that references files within the current source directory:

  generate_object_source(${CMAKE_CURRENT_SOURCE_DIR}/mydata.txt mydata.cpp)
  

• Finding Files
  You can leverage this variable to locate configuration files, data files, or other resources that are specific to the current source directory:

  configure_file(${CMAKE_CURRENT_SOURCE_DIR}/config.h.in ${CMAKE_CURRENT_BINARY_DIR}/config.h)
  

• Including Header Files
  You can use CMAKE_CURRENT_SOURCE_DIR to include header files that are located in the same directory as the current CMakeLists.txt:

  include_directories(${CMAKE_CURRENT_SOURCE_DIR}/include)
  

Advantages of Using CMAKE_CURRENT_SOURCE_DIR

• Flexibility
  It allows for dynamic behavior within the build system based on the current source directory.
• Maintainability
  Code becomes more readable and easier to maintain as file references are relative to the source directory structure.
• Portability
  It ensures consistent file paths across different operating systems.

In Summary

---

Including Header Files in Subdirectories

This example showcases including header files from a subdirectory named src relative to the current CMakeLists.txt:

# Top-level CMakeLists.txt

# Include header files from the src subdirectory
include_directories(${CMAKE_CURRENT_SOURCE_DIR}/src)

# Add an executable that uses the included headers
add_executable(my_program src/main.cpp)

Finding and Configuring Files

This example demonstrates finding a configuration file (config.h.in) in the current source directory and generating a configured version (config.h) in the build directory:

# CMakeLists.txt in a source directory

# Find the configuration file template
configure_file(${CMAKE_CURRENT_SOURCE_DIR}/config.h.in ${CMAKE_CURRENT_BINARY_DIR}/config.h)

# Add an executable that might use the generated configuration file
add_executable(my_program src/main.cpp)

Generating Code with Relative Paths

This example illustrates generating a C++ source file (data.cpp) dynamically based on a data file (mydata.txt) in the current source directory:

# CMakeLists.txt in a source directory

# Generate a C++ source file from a data file
generate_object_source(${CMAKE_CURRENT_SOURCE_DIR}/mydata.txt mydata.cpp)

# Add an executable that might use the generated data file
add_executable(my_program mydata.cpp)

---

Relative Paths

• Example
  

  # Assuming main.cpp and data.txt are in the same directory
  include_directories(./)  # Include current directory
  add_executable(my_program main.cpp data.txt)
  

• Limited Scope
  If you only need to reference files within the same directory or a limited subdirectory structure, relative paths can be simpler.

PROJECT_SOURCE_DIR and PROJECT_BINARY_DIR

• Example
  

  # Assuming config.h.in is in the top-level source directory
  configure_file(${PROJECT_SOURCE_DIR}/config.h.in ${CMAKE_CURRENT_BINARY_DIR}/config.h)
  

• Top-Level Scope
  These variables represent the absolute paths to the top-level source and binary directories, respectively. They are useful when referencing project-wide resources.

Custom Variables

• Example
  

  set(MY_DATA_DIR ${CMAKE_CURRENT_SOURCE_DIR}/data)
  find_file(MY_DATA_FILE NAMES mydata.txt PATHS ${MY_DATA_DIR})
  

• Flexibility
  Define your own variables to store specific paths or directory structures.

Choosing the Right Approach

The best alternative depends on your specific needs:

• Complex or Variable Paths
  Define custom variables for flexibility or handling dynamic structures.
• Project-Wide References
  Leverage PROJECT_SOURCE_DIR and PROJECT_BINARY_DIR for top-level resources.
• Simple Relative References
  Use relative paths for basic file inclusion within the same directory or subdirectories.

Additional Considerations

• Readability
  Keep your CMakeLists.txt easy to understand.
• Portability
  Ensure paths work on different operating systems.
• Maintainability
  Strive for clear and consistent path handling across your project.