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Add POSIX's C conversion specifier to printf funcs (#1276)

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POSIX specifies the C conversion specifier as being "equivalent to %lc",
i.e. printf("%C", arg) is equivalent in behaviour to printf("%lc", arg).

This patch implements this conversion specifier, and adds a test for it,
alongside another test, which ensures that va_arg uses the correct size,
even though we set signbit to 63 in the code (which one might think will
result in the wrong size of argument being va_arg-ed, but having signbit
set to 63 is in fact what __fmt_stoa expects and is a requirement for it
properly formatting the wchar_t argument - this does not result in wrong
usage of va_arg because the implementation of the c conversion specifier
(which the implementation of the C conversion specifier fallsthrough to)
always calls va_arg with an argument type of int, to avoid the very same
bug occuring with %lc, as the l length modifier also sets signbit to 63)
This commit is contained in:
Gabriel Ravier 2024-09-03 09:33:55 +02:00 • committed by GitHub
parent 3c61a541bd
commit 8f8145105c
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2 changed files with 33 additions and 0 deletions
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30
test/libc/stdio/snprintf_test.c
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@ -71,3 +71,33 @@ TEST(snprintf, testInf) {
for (i = 4; i < 10; ++i)
ASSERT_EQ(buf[i], '\0');
}
TEST(snprintf, testUppercaseCConversionSpecifier) {
char buf[10] = {};
int i = snprintf(buf, sizeof(buf), "%C", L'a');
ASSERT_EQ(i, 1);
ASSERT_STREQ(buf, "a");
i = snprintf(buf, sizeof(buf), "%C", L'☺');
ASSERT_EQ(i, 3);
ASSERT_STREQ(buf, "☺");
}
// Make sure we don't va_arg the wrong argument size on wide character
// conversion specifiers
TEST(snprintf,
testWideCConversionSpecifierWithLotsOfArgumentsBeforeAndOneAfter) {
char buf[20] = {};
int i = snprintf(buf, sizeof(buf), "%d%d%d%d%d%d%d%d%lc%d", 0, 0, 0, 0, 0, 0,
0, 0, L'x', 1);
ASSERT_EQ(i, 10);
ASSERT_STREQ(buf, "00000000x1");
memset(buf, 0, sizeof(buf));
i = snprintf(buf, sizeof(buf), "%d%d%d%d%d%d%d%d%C%d", 0, 0, 0, 0, 0, 0, 0, 0,
L'x', 1);
ASSERT_EQ(i, 10);
ASSERT_STREQ(buf, "00000000x1");
}