Compiler warnings on Debian 7 (Wheezy)

[ghost]

gcc-4.7.real (Debian 4.7.2-5) 4.7.2 with dpkg-buildflags

CFLAGS=-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security
CPPFLAGS=-D_FORTIFY_SOURCE=2
CXXFLAGS=-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security
FFLAGS=-g -O2
LDFLAGS=-Wl,-z,relro

shows:

gcc -DHAVE_CONFIG_H -I.  -D_GNU_SOURCE  -D_FORTIFY_SOURCE=2 -Wall -Werror -Wextra -g -O2 -fPIE -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security -c -o pick-pick.o `test -f 'pick.c' || echo './'`pick.c
pick.c: In function ‘xmbtowc’:
pick.c:1109:9: error: ignoring return value of ‘mbtowc’, declared with attribute warn_unused_result [-Werror=unused-result]

... looking at the code:

        n = mbtowc(wc, s, MB_CUR_MAX);
        if (n == -1) {
                mbtowc(NULL, NULL, MB_CUR_MAX);
                return 0;
        }

I don't understand why the second call to mbtowc is required here ...

[mptre]

I don't understand why the second call to mbtowc is required here ...

When in doubt, consult the manual; quoting mbtowc(3):

If a call to mbtowc() resulted in an undefined internal state,
mbtowc() must be called with s set to NULL to reset the internal state
before it can safely be used again.

Does a void suppress the warning?

diff --git pick.c pick.c
index d318a43..6ab2d9b 100644
--- pick.c
+++ pick.c
@@ -1106,7 +1106,7 @@ xmbtowc(wchar_t *wc, const char *s)
 
 	n = mbtowc(wc, s, MB_CUR_MAX);
 	if (n == -1) {
-		mbtowc(NULL, NULL, MB_CUR_MAX);
+		(void)mbtowc(NULL, NULL, MB_CUR_MAX);
 		return 0;
 	}

[ghost]

When in doubt, consult the manual; quoting mbtowc(3)

Sorry, but the paragraph you quoted is not in the manual here ...

Does a void suppress the warning?

No, but:

diff --git a/pick.c b/pick.c
index d318a43..28d0494 100644
--- a/pick.c
+++ b/pick.c
@@ -1106,7 +1106,7 @@ xmbtowc(wchar_t *wc, const char *s)
 
        n = mbtowc(wc, s, MB_CUR_MAX);
        if (n == -1) {
-               mbtowc(NULL, NULL, MB_CUR_MAX);
+               n = mbtowc(NULL, NULL, MB_CUR_MAX);
                return 0;
        }
 

[mptre]

Thanks, commited in 274969a.