https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70114
Bug ID: 70114
Summary: Incompatible implicit function prototype when
parameters match
Product: gcc
Version: 5.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: tanzx940228 at hotmail dot com
Target Milestone: ---
Created attachment 37883
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37883&action=edit
All the 3 examples shown in the comment.
Brief:
A function call in a scope where no prototype is given triggers an error, when
the parameters match a prototype given in a different scope.
Detail: I'm going to show 3 examples. The bug is shown in the 3rd example. All
3 examples are standalone .c files.
1.correct.c
-----------
int main() {
{
int foo(int arg);
foo(3);
}
{
int foo(float arg0, float arg1); // both gcc and clang get errors
return foo(3.0f, 4.0f);
}
}
Note that different prototypes are given in different scopes. Both gcc and
clang treat this as an error. This means they both think that a function can
only have one prototype throughout the translation unit - totally reasonable.
2.gcc.okay.c
------------
int main() {
{
int foo(int arg);
foo(3);
}
{
foo(3.0f, 4.0f); // gcc passes, clang gets an error
}
}
In this example, the second usage of 'foo' is in a scope with no prototype
given. Clang is smart enough to tell you that there is a prototype in another
scope, and the parameters in the call don't match that prototype. gcc compiles
this program (with a warning) - which is acceptable. Maybe gcc thinks that it's
the user's responsibility to check the parameters if he doesn't give a
prototype in the scope.
3.gcc.error.c
-------------
int main() {
{
int foo(float arg0, float arg1);
foo(3.0f, 4.0f);
}
{
foo(3.0f, 4.0f); // clang passes, gcc gets an error???
}
}
This is really weird! Clang gives me a warning saying that I'm using an
out-of-scope prototype. BUT gcc gives me an error, saying "incompatible
implicit declaration of function ‘foo’"! What happened?
I'm using:
gcc (Ubuntu 5.2.1-22ubuntu2) 5.2.1 20151010
Ubuntu clang version 3.6.2-1 (tags/RELEASE_362/final) (based on LLVM 3.6.2)
Target: x86_64-pc-linux-gnu
Thread model: posix
