# z_vcpkg_forward_output_variable

The latest version of this document lives in the [vcpkg repo](https://github.com/Microsoft/vcpkg/blob/master/docs/).

This macro helps with forwarding values from inner function calls,
through a local function scope, into pointer out parameters.

```cmake
z_vcpkg_forward_output_variable(ptr_to_parent_var var_to_forward)
```

is equivalent to

```cmake
if(DEFINED ptr_to_parent_var)
    if(DEFINED value_var)
        set("${ptr_to_parent_var}" "${value_var}" PARENT_SCOPE)
    else()
        unset("${ptr_to_parent_var}" PARENT_SCOPE)
    endif()
endif()
```

Take note that the first argument should be a local variable that has a value of the parent variable name.
Most commonly, this local is the result of a pointer-out parameter to a function.
If the variable in the first parameter is not defined, this function does nothing,
simplifying functions with optional out parameters.
Most commonly, this should be used in cases like:

```cmake
function(my_function out_var)
    file(SHA512 "somefile.txt" local_var)
    z_vcpkg_forward_output_variable(out_var local_var)
endfunction()
```

## Source
[scripts/cmake/z\_vcpkg\_forward\_output\_variable.cmake](https://github.com/Microsoft/vcpkg/blob/master/scripts/cmake/z_vcpkg_forward_output_variable.cmake)