Undefined behavior - C backend
Posted: Tue Feb 10, 2026 7:28 pm
Hi!
How does PureBasic C Backend compiler handles undefined behavior on the C generated code?
This PureBasic code:
Generated this C code in my test:
Both backends (asm and c) executed and resulted in the same output:
9223372036854775807
-9223372036854775808
But depending on the C compiler used and compilation flags the result can be different. So how is it handled or is it we should look out for?
How does PureBasic C Backend compiler handles undefined behavior on the C generated code?
This PureBasic code:
Code: Select all
EnableExplicit
OpenConsole()
Define i.i = $7FFFFFFFFFFFFFFF
PrintN(Str(i))
i + 1
PrintN(Str(i))
Input()
Code: Select all
// Define i.i = $7FFFFFFFFFFFFFFF
v_i=9223372036854775807;
//
// PrintN(Str(i))
SYS_PushStringBasePosition();
SYS_PushStringBasePosition();
SYS_PushStringBasePosition();
PB_Str(v_i,SYS_PopStringBasePosition());
void* p0=(void*)SYS_PopStringBasePositionValueNoUpdate();
integer rr1=PB_PrintN(p0);
SYS_PopStringBasePositionUpdate();
//
// i + 1
v_i=(v_i+1);
//
// PrintN(Str(i))
9223372036854775807
-9223372036854775808
But depending on the C compiler used and compilation flags the result can be different. So how is it handled or is it we should look out for?