CMake JSON array iteration

July 14, 2024

JSON can hold several data types including arrays. This example iterates over a JSON array in CMake.

Suppose file “json.cmake” contains:

cmake_minimum_required(VERSION 3.19)

set(jarr "{
\"c\":[3,4,5]
}")

string(JSON L LENGTH ${jarr} "c")
math(EXPR L "${L}-1")

string(JSON t TYPE ${jarr} "c")
message(STATUS "type: ${t}")

foreach(i RANGE ${L})
  string(JSON v GET ${jarr} "c" ${i})
  string(JSON t TYPE ${jarr} "c" ${i})
  message(STATUS "c[${i}] = ${v}  ${t}")
endforeach()

This results in:

$ cmake -P json.cmake

-- type: ARRAY
-- c[0] = 3  NUMBER
-- c[1] = 4  NUMBER
-- c[2] = 5  NUMBER