CMP0174 — CMake 4.2.6 Documentation

# CMP0174

Added in version 3.31.

`cmake_parse_arguments(PARSE_ARGV)` defines a variable for an empty string after a single-value keyword.

One of the main reasons for using the `PARSE_ARGV` form of the `cmake_parse_arguments()` command is to more robustly handle corner cases related to empty values. The non-`PARSE_ARGV` form doesn't preserve empty arguments, but the `PARSE_ARGV` form does. For each single-value keyword given, a variable should be defined if the keyword is present, even if it is followed by an empty string.

Prior to CMake 3.31, no variable would be defined if the value given after a single-value keyword was an empty string. This meant the code could not detect the difference between the keyword not being given, and it being given but with an empty value, except by iterating over all the arguments and checking if the keyword is present.

For the `OLD` behavior of this policy, `cmake_parse_arguments(PARSE_ARGV)` does not define a variable for a single-value keyword followed by an empty string, or followed by no value at all.

For the `NEW` behavior, `cmake_parse_arguments(PARSE_ARGV)` always defines a variable for each keyword given in the arguments, even a single-value keyword with an empty string as its value or no value at all. With the `NEW` behavior, the code can robustly check if a single-value keyword was given using just `if(DEFINED <prefix>_<keyword>)`.

This policy was introduced in CMake version 3.31. It may be set by `cmake_policy()` or `cmake_minimum_required()`. If it is not set, CMake warns, and uses `OLD` behavior.

Note

The `OLD` behavior of a policy is `deprecated by definition` and may be removed in a future version of CMake.