cmake error: string sub-command SUBSTRING requires four arguments

[TakC]

I am trying to get RInside implemented with Qt following the example available here. I am on macOS 12.6 using QT Creator 6.3.1.

Setting up the make file for cmake requires me to do a number of operations on strings so that QT knows where to find the necessary header files.

However, the line string(SUBSTRING ${RCPPFLAGS} ${NUM_TRUNC_CHARS} -1 RCPPFLAGS) throws an exception only inside of QT Creator, which says CMakeLists.txt:31: error: string sub-command SUBSTRING requires four arguments.

If I cmake (v3.24.2) the project directly from a terminal it compiles without problems and creates the correct substring operations.

Here is my CMakeLists.txt with some debug print statements.

make_minimum_required(VERSION 3.5)

project(rinside-clean LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

add_executable(rinside-clean main.cpp)

install(TARGETS rinside-clean
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR})

# print function to debug
function(PRINT_VAR VARNAME)
  message(STATUS "PRINT ${VARNAME}: ${${VARNAME}}")
endfunction()

execute_process(COMMAND R RHOME
                OUTPUT_VARIABLE R_HOME)

set(NUM_TRUNC_CHARS 2)

execute_process(COMMAND R CMD config --cppflags
                OUTPUT_VARIABLE RCPPFLAGS)

PRINT_VAR(RCPPFLAGS)

# this following line shows error: CMakeLists.txt:31: error: string sub-command SUBSTRING requires four arguments.
string(SUBSTRING ${RCPPFLAGS} ${NUM_TRUNC_CHARS} -1 RCPPFLAGS)

PRINT_VAR(RCPPFLAGS)
PRINT_VAR(NUM_TRUNC_CHARS)

include_directories(${RCPPFLAGS})

[...]

[Paul Colby]

Hi @TakC,

It's likel that either (or both) of ${RCPPFLAGS} and ${NUM_TRUNC_CHARS} are empty/unset. I'd suggest two things, depending on what suits your logic better.

Quote the args, so they're seen as "present" even if empty, like:

string(SUBSTRING "${RCPPFLAGS}" "${NUM_TRUNC_CHARS}" -1 RCPPFLAGS)

And/or, put some conditional checks in before that line to handle when those variables are empty/unset.

Cheers.

[TakC]

Thanks, it seems indeed as if the variables are not being set. This is odd, because both variables are always set when I run cmake for that project in my terminal. Only in Qt Creator it does not work.

[TakC]

Could there be any reason why the make file in Qt would not allow execute_process()?

It seems none of my calls return the output variables with a value, e.g.
execute_process(COMMAND R CMD config --cppflags OUTPUT_VARIABLE RCPPFLAGS).

In the terminal again, this returns the correct value.