Corrently handle buffer flush

fmtlib · Nov 9, 2024 · 521568d · 521568d
1 parent 5a3576a
commit 521568d
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Showing 2 changed files with 23 additions and 2 deletions.
diff --git a/include/fmt/format.h b/include/fmt/format.h
@@ -505,8 +505,8 @@ constexpr auto to_pointer(OutputIt, size_t) -> T* {
 template <typename T>
 FMT_CONSTEXPR20 auto to_pointer(basic_appender<T> it, size_t n) -> T* {
   buffer<T>& buf = get_container(it);
+  buf.try_reserve(buf.size() + n);
   auto size = buf.size();
-  buf.try_reserve(size + n);
   if (buf.capacity() < size + n) return nullptr;
   buf.try_resize(size + n);
   return buf.data() + size;

diff --git a/test/format-test.cc b/test/format-test.cc
@@ -1821,7 +1821,9 @@ TEST(format_test, big_print) {
 }
 
 // Windows CRT implements _IOLBF incorrectly (full buffering).
-#if FMT_USE_FCNTL && !defined(_WIN32)
+#if FMT_USE_FCNTL
+
+#ifndef _WIN32
 TEST(format_test, line_buffering) {
   auto pipe = fmt::pipe();
 
@@ -1847,6 +1849,25 @@ TEST(format_test, line_buffering) {
 }
 #endif
 
+TEST(format_test, buffer_boundary) {
+  auto pipe = fmt::pipe();
+
+  auto write_end = pipe.write_end.fdopen("w");
+  setvbuf(write_end.get(), nullptr, _IOFBF, 4096);
+  for(int i = 3 ; i < 4094 ; i++)
+      write_end.print("{}", (i % 73) != 0 ? 'x' : '\n');
+  write_end.print("{} {}", 1234, 567);
+  write_end.close();
+
+  auto read_end = pipe.read_end.fdopen("r");
+  char buf[4091] = {};
+  fread(buf, 1, sizeof(buf), read_end.get());
+  fgets(buf, sizeof(buf), read_end.get());
+  EXPECT_STREQ(buf, "1234 567");
+}
+
+#endif  // FMT_USE_FCNTL
+
 struct deadlockable {
   int value = 0;
   mutable std::mutex mutex;