From 119f7dc3d6dc02a07167a69a929cdfee9c0626e9 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <victor.zverovich@gmail.com>
Date: Fri, 27 Nov 2020 08:15:14 -0800
Subject: [PATCH] Truncate file by default

---
 include/fmt/os.h |  5 +++--
 test/os-test.cc  | 13 +++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/include/fmt/os.h b/include/fmt/os.h
index d945df47..f785c0a3 100644
--- a/include/fmt/os.h
+++ b/include/fmt/os.h
@@ -280,7 +280,8 @@ class file {
     WRONLY = FMT_POSIX(O_WRONLY),  // Open for writing only.
     RDWR = FMT_POSIX(O_RDWR),      // Open for reading and writing.
     CREATE = FMT_POSIX(O_CREAT),   // Create if the file doesn't exist.
-    APPEND = FMT_POSIX(O_APPEND)   // Open in append mode.
+    APPEND = FMT_POSIX(O_APPEND),  // Open in append mode.
+    TRUNC = FMT_POSIX(O_TRUNC)     // Truncate the content of the file.
   };
 
   // Constructs a file object which doesn't represent any file.
@@ -357,7 +358,7 @@ struct buffer_size {
 };
 
 struct ostream_params {
-  int oflag = file::WRONLY | file::CREATE;
+  int oflag = file::WRONLY | file::CREATE | file::TRUNC;
   size_t buffer_size = BUFSIZ > 32768 ? BUFSIZ : 32768;
 
   ostream_params() {}
diff --git a/test/os-test.cc b/test/os-test.cc
index 359b5ff8..ffe33d67 100644
--- a/test/os-test.cc
+++ b/test/os-test.cc
@@ -319,6 +319,19 @@ TEST(OStreamTest, BufferSize) {
   EXPECT_READ(in, "foo");
 }
 
+TEST(OStreamTest, Truncate) {
+  {
+    fmt::ostream out = fmt::output_file("test-file");
+    out.print("0123456789");
+  }
+  {
+    fmt::ostream out = fmt::output_file("test-file");
+    out.print("foo");
+  }
+  file in("test-file", file::RDONLY);
+  EXPECT_EQ("foo", read(in, 4));
+}
+
 TEST(FileTest, DefaultCtor) {
   file f;
   EXPECT_EQ(-1, f.descriptor());