gcc me harder: -Wconversion bug?

Sean Chittenden sean at chittenden.org
Tue Jun 10 02:21:31 PDT 2003

> It seems to me that this is doing exactly what is claimed for -Wconversion.
> To quote from the gcc man page:
>        -Wconversion
>               Warn  if  a prototype causes a type conversion that
>               is different from what would happen to the same ar-
>               gument  in  the  absence  of a prototype.  ...
> Now in the absence of a prototype for f() the argument true would be
> promoted from char/bool to int before being passed to the
> function. With the prototype in scope it is not promoted. Different
> argument widths so warning delivered.

% cpp test.c
# 1 "test7.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "test7.c"
# 1 "test7.h" 1
# 13 "test7.h"
void f(char b);
# 2 "test7.c" 2

main(int argc, char *argv[]) {


f(char b) {

Am I missing something that says that there isn't the prototype of the
same width?  Last time I checked my vision, f(char b) was the same as
f(char b)...  :-/ or am I missing something?  I believe that gcc's
promoting the char to an int or to some other non-1 byte width data
type... but I'm not seeing how, where, or why.  -sc

Sean Chittenden

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