QUERY · ISSUE

cannot open source file "alloca.h" when trying to write a C module for MicroPython

openby marrowbusteropened 2025-05-09updated 2025-07-14

bugneeds-info

Port, board and/or hardware

rp2 port, Waveshare RP2040-PiZero

MicroPython version

MicroPython v1.25.0 on 2025-04-15; Raspberry Pi Pico with RP2040

Reproduction

Was working on a C module file for MicroPython and included this repo as a submodule but when it got time to #includeing the necessary header files, I got the above error. Apparently it's because alloca.h is only present on Linux and I'm using VSCode on Windows with the MicroPico extension. How shall I remedy this?

Expected behaviour

No response

Observed behaviour

Hovering over the #include "py/runtime.h" file leads to the error cannot open source file "alloca.h" being shown.

Additional Information

No, I've provided everything above.

Code of Conduct

Yes, I agree

CANDIDATE · PULL REQUEST

py: Use <alloca.h> for alloca()

mergedby stinosopened 2014-05-03updated 2014-07-10

alloca() is declared in alloca.h which als happens to be included by stdlib.h.
For mingw however it resides in malloc.h only.
So if we include alloca.h directly, and add an alloca.h for mingw in it's port
directory we can get rid of the mingw-specific define to include malloc.h
and the other ports are happy as well.

Assessment

S Sonnet · medium

Both involve alloca.h availability on Windows, but the scope differs. PR #552 adds a windows/alloca.h wrapper to fix alloca() includes in py/builtinimport.c and py/objfun.c within the MicroPython core. The query issue is about VSCode IntelliSense failing to locate alloca.h when a user includes py/runtime.h in an external C module — an IDE configuration/IntelliSense path problem, not a build failure in the core. PR #552's windows/alloca.h only redirects to malloc.h for MinGW builds; it does not configure IntelliSense include paths or address user C module development on Windows. Even if PR #552 is merged, the query reporter's VSCode environment would still fail to find alloca.h unless the include path is configured correctly for the IDE.

Suggested action

Leave open. Inform the reporter that this is a VSCode IntelliSense configuration issue, not a build problem. They need to configure their c_cpp_properties.json (or equivalent) to include the correct SDK include paths for Windows. PR #552 addresses a different (core-internal) alloca.h inclusion issue and does not resolve this report.