# Segfault passing a map array by value
**URL:** https://community.freefem.org/t/segfault-passing-a-map-array-by-value/4016
**Category:** General Discussion
**Created:** [July 25, 2025, 7:33am UTC](https://community.freefem.org/t/segfault-passing-a-map-array-by-value/4016 "2025-07-25T07:33:01Z")
**Posts on this page:** 1
**Page:** 1
### Author:  [@jtermens](https://community.freefem.org/u/jtermens)
#### Post date: [July 25, 2025, 7:33am UTC](https://community.freefem.org/t/segfault-passing-a-map-array-by-value/4016/1 "2025-07-25T07:33:02Z")
Hi everyone,
I’ve been exploring different ways to encapsulate mesh creation in FreeFem++ (version 4.15), experimenting with the available data types. My goal is to build a catalog of functions, each of which takes a structure containing mesh parameters and returns a different mesh. While the parameters may vary between meshes, the structure should remain consistent.
I’ve tested passing the mesh parameters as an array:
`func mesh meshFunction(real[int] meshParameters)`
and as a dictionary (dynamic map):
`func mesh meshFunction(real[string] meshParameters)`
Passing an array works as expected and the script exits without error. However, passing a real[string] map causes a segmentation fault. After some testing, I noticed that both function definitions pass their arguments by value. I then tried passing the real[string] map by reference:
`func mesh meshFunction(real[string]& meshParameters)`
and it worked. 🙂
I suspect there might be an issue with how `map` is copied when passed by value, potentially causing a segmentation fault at the level of the virtual machine. I’m not sure whether this is a known issue, but I thought I’d share it in case it’s helpful to others encountering similar problems.
I’ve attached a minimal working example below.
[mesh\_dict.edp](https://community.freefem.org/uploads/short-url/sCm9rkPeh8w09ydIm5hHuPVJer.edp) (1.9 KB)