From ed97d9a3a201cda4f99fb19c7fce5df9209a5d72 Mon Sep 17 00:00:00 2001
From: fhgffy <102001626+fhgffy@users.noreply.github.com>
Date: Thu, 8 Oct 2026 23:56:57 +0800
Subject: [PATCH] Ignore '+' and space flags for unsigned printf conversions

C only applies the '+' and space flags to signed conversions, so
fmt::sprintf("%+u", 42) should give "42" like printf does, not "+42".
The same goes for %o, %x and %X.
---
 include/fmt/printf.h |  3 +++
 test/printf-test.cc  | 14 ++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/fmt/printf.h b/include/fmt/printf.h
index e25e6fba..03c8746d 100644
--- a/include/fmt/printf.h
+++ b/include/fmt/printf.h
@@ -545,6 +545,9 @@ void vprintf(buffer<Char>& buf, basic_string_view<Char> format,
     if (it == end) report_error("invalid format string");
     char type = static_cast<char>(*it++);
     if (is_integral_type(arg.type())) {
+      // The '+' and space flags only apply to signed conversions.
+      if (type == 'u' || type == 'o' || type == 'x' || type == 'X')
+        specs.set_sign(sign::none);
       // Normalize type.
       switch (type) {
       case 'i':
diff --git a/test/printf-test.cc b/test/printf-test.cc
index f8322522..e2a06f8d 100644
--- a/test/printf-test.cc
+++ b/test/printf-test.cc
@@ -169,6 +169,14 @@ TEST(printf_test, plus_flag) {
   // '+' flag and space flag are both ignored for non-numeric types.
   EXPECT_PRINTF("x", "%+ c", 'x');
   EXPECT_PRINTF("x", "% +c", 'x');
+
+  // '+' flag is ignored for unsigned conversions.
+  EXPECT_PRINTF("42", "%+u", 42);
+  EXPECT_PRINTF("42", "%+o", 042);
+  EXPECT_PRINTF("2a", "%+x", 0x2a);
+  EXPECT_PRINTF("2A", "%+X", 0x2a);
+  EXPECT_PRINTF("0x002a", "%+#06x", 0x2a);
+  EXPECT_PRINTF("", "%+.0u", 0);
 }
 
 TEST(printf_test, minus_flag) {
@@ -199,6 +207,12 @@ TEST(printf_test, space_flag) {
 
   // ' ' flag is ignored for non-numeric types.
   EXPECT_PRINTF("x", "% c", 'x');
+
+  // ' ' flag is ignored for unsigned conversions.
+  EXPECT_PRINTF("42", "% u", 42);
+  EXPECT_PRINTF("42", "% o", 042);
+  EXPECT_PRINTF("0002a", "% 05x", 0x2a);
+  EXPECT_PRINTF("2A", "% X", 0x2a);
 }
 
 TEST(printf_test, hash_flag) {