# Multi-file builds and the standard library

Part of the [pitfalls index](../PITFALLS.md).

- **Multi-file extensions.** INCLUDE imports symbols, never text; every included file
  must also be an input.
  - Duplicate exports across files fail even without visibility, except distinct
    signatures whose definitions all specify OVERLOAD.
  - Only one file may contain top-level code; top-level DECLARE is a main local, not
    an export.
  - Definitions-only builds fail without FUNCTION MAIN returning INTEGER. MAIN
    cannot coexist with top-level code.
  - GLOBAL accepts only the five primitive scalar types and literal initializers;
    arrays, user types and computed initializers are rejected.
  - Own top-level constants remain positional, imported constants do not.
- **Default standard library.** std.cps and its imported STRING library are embedded
  and automatically linked.
  - Use -no-std before explicitly supplying a replacement STRING class/library;
    otherwise duplicate definitions fail.
  - Ordinary literals require a visible STRING class with NEW(C_STRING).
  - C_TYPE/INCLUDE/EXTERN syntax strings are parser metadata and do not construct
    STRING.
  - -S emits IR only; manual linking needs string.o and the C++ runtime.