* RFC: why do our std::ofsteam functions add ios_base::trunc ?
@ 2017-10-24 18:25 Jonathan Wakely
2017-10-30 15:36 ` Jonathan Wakely
0 siblings, 1 reply; 2+ messages in thread
From: Jonathan Wakely @ 2017-10-24 18:25 UTC (permalink / raw)
To: libstdc++, gcc-patches
[-- Attachment #1: Type: text/plain, Size: 700 bytes --]
While adding the new C++17 overloads taking filesystem paths to
<fstream> I noticed that ofstream uses out|trunc for the default
arguments instead of out as the stadnard says. The effect is the same,
but my preference would be to do what the standard says. Is there a
good reason for deviating from what the standard says?
Although the out|trunc default arguments have no difference in
behaviour from just using out, the comments saying
"Calls @c std::basic_filebuf::open(__s,__mode|out|trunc)"
are definitely wrong. That would not be a conforming behaviour.
Also, I think we can remove the comments saying to use c_str() as
fstreams accept std::string arguments since C++11.
Any comments?
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[-- Type: text/x-patch, Size: 4879 bytes --]
diff --git a/libstdc++-v3/include/std/fstream b/libstdc++-v3/include/std/fstream
index 52830945fe2..db41a697085 100644
--- a/libstdc++-v3/include/std/fstream
+++ b/libstdc++-v3/include/std/fstream
@@ -487,9 +487,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @param __mode Open file in specified mode (see std::ios_base).
*
* @c ios_base::in is automatically included in @a __mode.
- *
- * Tip: When using std::string to hold the filename, you must use
- * .c_str() before passing it to this constructor.
*/
explicit
basic_ifstream(const char* __s, ios_base::openmode __mode = ios_base::in)
@@ -587,9 +584,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
*
* Calls @c std::basic_filebuf::open(s,__mode|in). If that function
* fails, @c failbit is set in the stream's error state.
- *
- * Tip: When using std::string to hold the filename, you must use
- * .c_str() before passing it to this constructor.
*/
void
open(const char* __s, ios_base::openmode __mode = ios_base::in)
@@ -687,15 +681,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @param __s Null terminated string specifying the filename.
* @param __mode Open file in specified mode (see std::ios_base).
*
- * @c ios_base::out | @c ios_base::trunc is automatically included in
- * @a __mode.
- *
- * Tip: When using std::string to hold the filename, you must use
- * .c_str() before passing it to this constructor.
+ * @c ios_base::out is automatically included in @a __mode.
*/
explicit
basic_ofstream(const char* __s,
- ios_base::openmode __mode = ios_base::out|ios_base::trunc)
+ ios_base::openmode __mode = ios_base::out)
: __ostream_type(), _M_filebuf()
{
this->init(&_M_filebuf);
@@ -708,12 +698,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @param __s std::string specifying the filename.
* @param __mode Open file in specified mode (see std::ios_base).
*
- * @c ios_base::out | @c ios_base::trunc is automatically included in
- * @a __mode.
+ * @c ios_base::out is automatically included in @a __mode.
*/
explicit
basic_ofstream(const std::string& __s,
- ios_base::openmode __mode = ios_base::out|ios_base::trunc)
+ ios_base::openmode __mode = ios_base::out)
: __ostream_type(), _M_filebuf()
{
this->init(&_M_filebuf);
@@ -789,15 +778,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @param __s The name of the file.
* @param __mode The open mode flags.
*
- * Calls @c std::basic_filebuf::open(__s,__mode|out|trunc). If that
+ * Calls @c std::basic_filebuf::open(__s,__mode|out). If that
* function fails, @c failbit is set in the stream's error state.
- *
- * Tip: When using std::string to hold the filename, you must use
- * .c_str() before passing it to this constructor.
*/
void
- open(const char* __s,
- ios_base::openmode __mode = ios_base::out | ios_base::trunc)
+ open(const char* __s, ios_base::openmode __mode = ios_base::out)
{
if (!_M_filebuf.open(__s, __mode | ios_base::out))
this->setstate(ios_base::failbit);
@@ -813,12 +798,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @param __s The name of the file.
* @param __mode The open mode flags.
*
- * Calls @c std::basic_filebuf::open(s,mode|out|trunc). If that
+ * Calls @c std::basic_filebuf::open(s,mode|out). If that
* function fails, @c failbit is set in the stream's error state.
*/
void
- open(const std::string& __s,
- ios_base::openmode __mode = ios_base::out | ios_base::trunc)
+ open(const std::string& __s, ios_base::openmode __mode = ios_base::out)
{
if (!_M_filebuf.open(__s, __mode | ios_base::out))
this->setstate(ios_base::failbit);
@@ -894,9 +878,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @brief Create an input/output file stream.
* @param __s Null terminated string specifying the filename.
* @param __mode Open file in specified mode (see std::ios_base).
- *
- * Tip: When using std::string to hold the filename, you must use
- * .c_str() before passing it to this constructor.
*/
explicit
basic_fstream(const char* __s,
@@ -993,9 +974,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
*
* Calls @c std::basic_filebuf::open(__s,__mode). If that
* function fails, @c failbit is set in the stream's error state.
- *
- * Tip: When using std::string to hold the filename, you must use
- * .c_str() before passing it to this constructor.
*/
void
open(const char* __s,
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: RFC: why do our std::ofsteam functions add ios_base::trunc ?
2017-10-24 18:25 RFC: why do our std::ofsteam functions add ios_base::trunc ? Jonathan Wakely
@ 2017-10-30 15:36 ` Jonathan Wakely
0 siblings, 0 replies; 2+ messages in thread
From: Jonathan Wakely @ 2017-10-30 15:36 UTC (permalink / raw)
To: libstdc++, gcc-patches
[-- Attachment #1: Type: text/plain, Size: 906 bytes --]
On 24/10/17 19:25 +0100, Jonathan Wakely wrote:
>While adding the new C++17 overloads taking filesystem paths to
><fstream> I noticed that ofstream uses out|trunc for the default
>arguments instead of out as the stadnard says. The effect is the same,
>but my preference would be to do what the standard says. Is there a
>good reason for deviating from what the standard says?
>
>Although the out|trunc default arguments have no difference in
>behaviour from just using out, the comments saying
>
> "Calls @c std::basic_filebuf::open(__s,__mode|out|trunc)"
>
>are definitely wrong. That would not be a conforming behaviour.
>
>Also, I think we can remove the comments saying to use c_str() as
>fstreams accept std::string arguments since C++11.
>
>Any comments?
I've removed these redundant bits from the default arguments, and from
the misleading comments.
Tested powerpc64le-linux, committed to trunk.
[-- Attachment #2: patch.txt --]
[-- Type: text/x-patch, Size: 6206 bytes --]
commit 892871f7c6259919aecfb197ea69c013d9c19cb2
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Mon Oct 30 15:00:49 2017 +0000
Remove ios_mode::trunc from basic_ofstream openmode arguments
* include/std/fstream (basic_ifstream, basic_ofstream, basic_fstream):
Remove outdated comments about calling c_str() to create a file stream
from a std::string.
(basic_ofstream::basic_ofstream, basic_ofstream::open): Remove
redundant ios_mode::trunc bits from default arguments and comments.
diff --git a/libstdc++-v3/include/std/fstream b/libstdc++-v3/include/std/fstream
index 3205f81fb47..a3324c004d7 100644
--- a/libstdc++-v3/include/std/fstream
+++ b/libstdc++-v3/include/std/fstream
@@ -506,9 +506,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @param __mode Open file in specified mode (see std::ios_base).
*
* @c ios_base::in is automatically included in @a __mode.
- *
- * Tip: When using std::string to hold the filename, you must use
- * .c_str() before passing it to this constructor.
*/
explicit
basic_ifstream(const char* __s, ios_base::openmode __mode = ios_base::in)
@@ -622,9 +619,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
*
* Calls @c std::basic_filebuf::open(s,__mode|in). If that function
* fails, @c failbit is set in the stream's error state.
- *
- * Tip: When using std::string to hold the filename, you must use
- * .c_str() before passing it to this constructor.
*/
void
open(const char* __s, ios_base::openmode __mode = ios_base::in)
@@ -738,15 +732,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @param __s Null terminated string specifying the filename.
* @param __mode Open file in specified mode (see std::ios_base).
*
- * @c ios_base::out | @c ios_base::trunc is automatically included in
- * @a __mode.
- *
- * Tip: When using std::string to hold the filename, you must use
- * .c_str() before passing it to this constructor.
+ * @c ios_base::out is automatically included in @a __mode.
*/
explicit
basic_ofstream(const char* __s,
- ios_base::openmode __mode = ios_base::out|ios_base::trunc)
+ ios_base::openmode __mode = ios_base::out)
: __ostream_type(), _M_filebuf()
{
this->init(&_M_filebuf);
@@ -759,12 +749,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @param __s std::string specifying the filename.
* @param __mode Open file in specified mode (see std::ios_base).
*
- * @c ios_base::out | @c ios_base::trunc is automatically included in
- * @a __mode.
+ * @c ios_base::out is automatically included in @a __mode.
*/
explicit
basic_ofstream(const std::string& __s,
- ios_base::openmode __mode = ios_base::out|ios_base::trunc)
+ ios_base::openmode __mode = ios_base::out)
: __ostream_type(), _M_filebuf()
{
this->init(&_M_filebuf);
@@ -777,13 +766,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @param __s filesystem::path specifying the filename.
* @param __mode Open file in specified mode (see std::ios_base).
*
- * @c ios_base::out | @c ios_base::trunc is automatically included in
- * @a __mode.
+ * @c ios_base::out is automatically included in @a __mode.
*/
template<typename _Path, typename = _Require<
is_constructible<__filebuf_type, const _Path&, ios_base::openmode>>>
- basic_ofstream(const _Path& __s, ios_base::openmode __mode
- = ios_base::out|ios_base::trunc)
+ basic_ofstream(const _Path& __s,
+ ios_base::openmode __mode = ios_base::out)
: basic_ofstream(__s.c_str(), __mode)
{ }
#endif // C++17
@@ -857,15 +845,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @param __s The name of the file.
* @param __mode The open mode flags.
*
- * Calls @c std::basic_filebuf::open(__s,__mode|out|trunc). If that
+ * Calls @c std::basic_filebuf::open(__s,__mode|out). If that
* function fails, @c failbit is set in the stream's error state.
- *
- * Tip: When using std::string to hold the filename, you must use
- * .c_str() before passing it to this constructor.
*/
void
- open(const char* __s,
- ios_base::openmode __mode = ios_base::out | ios_base::trunc)
+ open(const char* __s, ios_base::openmode __mode = ios_base::out)
{
if (!_M_filebuf.open(__s, __mode | ios_base::out))
this->setstate(ios_base::failbit);
@@ -881,12 +865,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @param __s The name of the file.
* @param __mode The open mode flags.
*
- * Calls @c std::basic_filebuf::open(s,mode|out|trunc). If that
+ * Calls @c std::basic_filebuf::open(s,mode|out). If that
* function fails, @c failbit is set in the stream's error state.
*/
void
- open(const std::string& __s,
- ios_base::openmode __mode = ios_base::out | ios_base::trunc)
+ open(const std::string& __s, ios_base::openmode __mode = ios_base::out)
{
if (!_M_filebuf.open(__s, __mode | ios_base::out))
this->setstate(ios_base::failbit);
@@ -978,9 +961,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @brief Create an input/output file stream.
* @param __s Null terminated string specifying the filename.
* @param __mode Open file in specified mode (see std::ios_base).
- *
- * Tip: When using std::string to hold the filename, you must use
- * .c_str() before passing it to this constructor.
*/
explicit
basic_fstream(const char* __s,
@@ -1091,9 +1071,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
*
* Calls @c std::basic_filebuf::open(__s,__mode). If that
* function fails, @c failbit is set in the stream's error state.
- *
- * Tip: When using std::string to hold the filename, you must use
- * .c_str() before passing it to this constructor.
*/
void
open(const char* __s,
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2017-10-30 15:36 ` Jonathan Wakely
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