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.