CMake: Looping through a string and getting the fi

Question

I'm trying to write a CMake script that does the following:

Using the execute_process instruction reads the output of a command and stores it into a variable named 'STRING_VARIABLE'. The command that returns something that has both characters and digits in it's name. Something like this: RESULT-v1.2.8-...

I have read this value properly and displayed it on the terminal to confirm this. Now what I want to do is store the first three digits of this output and store them in 3 other variables: 'FIRST_DIGIT', 'SECOND_DIGIT' and 'THIRD_DIGIT'.

My logic was this: Using a counter count each time a digit is encountered in a variable name. Each time a digit is encountered store the digit in one of the three variables then increment the counter. The counter counts therefore from 0 to 2 and for each of these 3 values does a store.

Here is the script I wrote:

SET(COUNTER 0)
foreach(LETTER ${STRING_VARIABLE})
       if(LETTER EQUAL '0,1,2,3,4,5,6,7,8,9')

        if( COUNTER EQUAL 0 )                                 # if first digit is encountered
         list(GET STRING_VARIABLE LETTER FIRST_DIGIT)        # store it in FIRST_DIGIT
         SET(COUNTER 1) 
        elseif( COUNTER EQUAL 1 )                             # if second digit is encountered
         list(GET STRING_VARIABLE LETTER SECOND_DIGIT)        # store it in SECOND_DIGIT
         SET(COUNTER 2)
        else( COUNTER EQUAL 2 )                               # if second digit is encountered
         list(GET STRING_VARIABLE LETTER THIRD_DIGIT)        # store it in THIRD_DIGIT
        endif()

       endif()

endforeach()

# To check the variables

#message("*****${STRING_VARIABLE}") # OK!
message("*****${FIRST_DIGIT}")      # NOT OK :(

As I'm a total beginner in CMake I suppose my problem is at either of the two(or both): - When looping through the 'STRING_VARIABLE' I used foreach(LETTER) and since my string also contains digits the program may not see them. If that is the mistake with what else should I replace LETTER in order to get each character of the string? - In the first if where I check if the 'LETTER' is a digit. I think that is the correct syntax altough I'm not sure. Basically what I'm doing there is trying to check if the letter at each index is a digit.

The 'STRING_VARIABLE' prints ok as I said. However when I try printing the 'FIRST_DIGIT' or any other of the 3(second and third) I get an empty string as a result. Please help me understand what is wrong in my logic and what I'm doing wrong.

Please help me understand what I'm doing wrong. Thank you.

Answer 1

In case the format is know, you can use string(REGEX REPLACE ...).

Function:

function(get_versions versionstring libname major minor patch)
    string(REGEX REPLACE "([A-Za-z0-9_]*)-[vV].*" "\\1" locallibname ${versionstring} )
    set(libname ${locallibname} PARENT_SCOPE)
    string(REGEX REPLACE "^([A-Za-z0-9_]*-[vV])([0-9]*)([.][0-9]*[.][0-9]*-?.*)$" "\\2" numbers ${versionstring} )
    set(major ${numbers} PARENT_SCOPE)
    string(REGEX REPLACE "^([A-Za-z0-9_]*-[vV][0-9]*[.])([0-9]*)([.][0-9]*-?.*)$" "\\2" numbers ${versionstring} )
    set(minor ${numbers} PARENT_SCOPE)
    string(REGEX REPLACE "^([A-Za-z0-9_]*-[vV][0-9]*[.][0-9]*[.])([0-9]*)(-?.*)$" "\\2" numbers ${versionstring} )
    set(patch ${numbers} PARENT_SCOPE)
endfunction()

Usage:

get_versions("MyLib-V11.222.034-remark" libname major minor patch)
status_ref(libname)
status_ref(major)
status_ref(minor)
status_ref(patch)

Result:

STATUS: libname = "MyLib"
STATUS: major = "11"
STATUS: minor = "222"
STATUS: patch = "034"