打开fstream的问题 [英] problem opening fstream
问题描述
使用RH9，来自这个片段：
fstream theStream_;
string fPath =" myFile";
int mode = O_EXCL | O_CREAT;
theStream_.open（fPath.c_str（），mode）;
我得到的失败如下所示。根据手册页和
标准，第二个参数应该是int。
预先感谢您的帮助。
迈克。
-
g ++ -I。 -I ../ MdbUtil -c -o UniqueFile.o UniqueFile.cc
UniqueFile.cc：在成员函数`void MdbUtil :: UniqueFile :: open（const char *，
const char *，int，int，const char *）''：
UniqueFile.cc:64：从`int''无效转换为`std :: _ Ios_Openmode''
UniqueFile.cc:64：初始化`void std :: basic_fstream< _CharT，
_Traits> :: open（const char *，std :: _ Ios_Openmode）的参数2 [与_CharT = char，_Traits
= std :: char_traits< char>]''
make：*** [UniqueFile.o]错误1
" Mike - EMAIL IGNORED" < M _ ************* @ yahoo.com>写了...使用RH9，来自这个片段：
fstream theStream_;
string fPath =" myFile" ;;
int mode = O_EXCL | O_CREAT;
theStream_.open（fPath.c_str（），mode）;
什么是'O_EXCL | O_CREAT''表达''fstream :: open''？
你应该使用''std :: ios_base''中的常量......
我得到如下所示的失败。根据手册页和标准，第二个参数应该是int。
根据什么标准？什么页面/子句/段落？我的
标准副本声明第二个参数的类型为
''std :: ios_base :: openmode''。
谢谢提前帮助。
迈克。
-
g ++ -I。 -I ../ MdbUtil -c -o UniqueFile.o UniqueFile.cc
UniqueFile.cc：在成员函数`void MdbUtil :: UniqueFile :: open（const
char *，const char *，int ，int，const char *）''：
UniqueFile.cc：64：从`int''无效转换为`std :: _ Ios_Openmode''
UniqueFile.cc：64：初始化参数2的` void
std :: basic_fstream< _CharT，_Traits> :: open（const char *，std :: _ Ios_Openmode）[with _CharT = char，
_Traits = std :: char_traits< char>]''
make：*** [UniqueFile.o]错误1
是的，我现在看到了我的错误。我的要求是打开一个ofstream，
，如果文件已经存在则让它失败。我查看了std :: ios_base中的
常量，就像旧的fstream功能一样，
它似乎没有语义来执行此操作。如果我对此有正确的判断，那么检查文件存在的最佳方法是什么？
再次感谢您的帮助，
Mike。
Victor Bazarov写道：
Mike - EMAIL IGNORED < M _ ************* @ yahoo.com>写了...使用RH9，来自这个片段：
fstream theStream_;
string fPath =" myFile" ;;
int mode = O_EXCL | O_CREAT;
theStream_.open（fPath.c_str（），mode）;
'O_EXCL是什么| O_CREAT''表达式在''fstream :: open''吗？
你应该使用''std :: ios_base''中的常量......
<我得到了下面显示的失败。根据手册页和标准，第二个参数应该是一个int。
根据什么标准？什么页面/子句/段落？我的
标准副本声明第二个参数的类型为
''std :: ios_base :: openmode''。
提前感谢您的支持麦克。
-I ../ MdbUtil -c -o UniqueFile.o UniqueFile.cc
UniqueFile.cc：在成员函数`void MdbUtil :: UniqueFile :: open（const
char *，< blockquote class =post_quotes> const char *，int，int，const char *）''：
UniqueFile.cc：64：从`int''无效转换为`std :: _ Ios_Openmode'' UniqueFile.cc:64：初始化`void的参数2
std :: basic_fstream< _CharT，_Traits> :: open（const char *，std :: _ Ios_Openmode ）[with _CharT = char，
_Traits= std :: char_traits< char>]''
make：*** [UniqueFile.o]错误1
" Mike - EMAIL IGNORED" < M _ ************* @ yahoo.com>写道：Victor Bazarov写道：
Mike - EMAIL IGNORED < M _ ************* @ yahoo.com>写了...使用RH9，来自这个片段：
fstream theStream_;
string fPath =" myFile" ;;
int mode = O_EXCL | O_CREAT;
theStream_.open（fPath.c_str（），mode）;
'O_EXCL是什么| O_CREAT''表达式在''fstream :: open''吗？
你应该使用''std :: ios_base''中的常量......
<我得到了下面显示的失败。根据手册页和标准，第二个参数应该是一个int。
根据什么标准？什么页面/子句/段落？我的
标准副本声明第二个参数的类型为
''std :: ios_base :: openmode''。
提前感谢您的支持麦克。
-I ../ MdbUtil -c -o UniqueFile.o UniqueFile.cc
UniqueFile.cc：在成员函数中`void
MdbUtil :: UniqueFile :: open（constchar *，const char *，int，int，const char *）''：
UniqueFile.cc：64：从`int'转换无效'to
`std :: _ Ios_Openmode''UnityFile.cc:64：初始化`void的参数2
std :: basic_fstream< _CharT，_Traits> :: open（const char *，std :: _ Ios_Openmode）[with _CharT =
char，_Traits= std :: char_traits< char>]''
make：*** [UniqueFile.o]错误1
是的，我看到了我的现在错了。我的要求是打开一个ofstream，
如果文件已经存在则让它失败。我查看了std :: ios_base中的
常量，并且像旧的fstream功能一样，
它似乎没有语义来执行此操作。如果我对此是正确的，检查文件存在的最佳方法是什么？
（a）请不要't top-post
（b）我在C ++中知道检查文件是否存在的唯一方法是打开
文件进行阅读[只有]并检查它是否成功。我的
猜测如果它没有成功（没有这样的文件），那么
你重新打开流写进行并继续使用它（如果我
正确理解你的意图。
Victor
Using RH9, from this fragment:
fstream theStream_;
string fPath = "myFile";
int mode = O_EXCL | O_CREAT;
theStream_.open(fPath.c_str(),mode);
I get the failure shown below. According to the man pages and
the standard, the second argument should be an int.
Thanks in advance for your help.
Mike.
--
g++ -I. -I../MdbUtil -c -o UniqueFile.o UniqueFile.cc
UniqueFile.cc: In member function `void MdbUtil::UniqueFile::open(const char*,
const char*, int, int, const char*)'':
UniqueFile.cc:64: invalid conversion from `int'' to `std::_Ios_Openmode''
UniqueFile.cc:64: initializing argument 2 of `void std::basic_fstream<_CharT,
_Traits>::open(const char*, std::_Ios_Openmode) [with _CharT = char, _Traits
= std::char_traits<char>]''
make: *** [UniqueFile.o] Error 1
"Mike - EMAIL IGNORED" <m_*************@yahoo.com> wrote...Using RH9, from this fragment:
fstream theStream_;
string fPath = "myFile";
int mode = O_EXCL | O_CREAT;
theStream_.open(fPath.c_str(),mode);
What does ''O_EXCL | O_CREAT'' expression doing in ''fstream::open''?
You are supposed to use constants from ''std::ios_base''...
I get the failure shown below. According to the man pages and
the standard, the second argument should be an int.
According to what standard? What page/clause/paragraph? My copy of the
standard states that the second argument has the type
''std::ios_base::openmode''.
Thanks in advance for your help.
Mike.
--
g++ -I. -I../MdbUtil -c -o UniqueFile.o UniqueFile.cc
UniqueFile.cc: In member function `void MdbUtil::UniqueFile::open(const char*, const char*, int, int, const char*)'':
UniqueFile.cc:64: invalid conversion from `int'' to `std::_Ios_Openmode''
UniqueFile.cc:64: initializing argument 2 of `void std::basic_fstream<_CharT, _Traits>::open(const char*, std::_Ios_Openmode) [with _CharT = char, _Traits = std::char_traits<char>]''
make: *** [UniqueFile.o] Error 1
Yes, I see my error now. My requirement is to open an ofstream,
and have it fail if the file already exists. I looked at the
constants in std::ios_base, and like the old fstream capability,
it does not appear to have the semantics to do this. If I am
correct about this, what is the best way to check for the
existence of a file?
Thanks again for your help,
Mike.
Victor Bazarov wrote:
"Mike - EMAIL IGNORED" <m_*************@yahoo.com> wrote...Using RH9, from this fragment:
fstream theStream_;
string fPath = "myFile";
int mode = O_EXCL | O_CREAT;
theStream_.open(fPath.c_str(),mode);
What does ''O_EXCL | O_CREAT'' expression doing in ''fstream::open''?
You are supposed to use constants from ''std::ios_base''...
I get the failure shown below. According to the man pages and
the standard, the second argument should be an int.
According to what standard? What page/clause/paragraph? My copy of the
standard states that the second argument has the type
''std::ios_base::openmode''.Thanks in advance for your help.
Mike.
--
g++ -I. -I../MdbUtil -c -o UniqueFile.o UniqueFile.cc
UniqueFile.cc: In member function `void MdbUtil::UniqueFile::open(const
char*,const char*, int, int, const char*)'':
UniqueFile.cc:64: invalid conversion from `int'' to `std::_Ios_Openmode''
UniqueFile.cc:64: initializing argument 2 of `void
std::basic_fstream<_CharT,_Traits>::open(const char*, std::_Ios_Openmode) [with _CharT = char,
_Traits= std::char_traits<char>]''
make: *** [UniqueFile.o] Error 1
"Mike - EMAIL IGNORED" <m_*************@yahoo.com> wrote...Victor Bazarov wrote:
"Mike - EMAIL IGNORED" <m_*************@yahoo.com> wrote...Using RH9, from this fragment:
fstream theStream_;
string fPath = "myFile";
int mode = O_EXCL | O_CREAT;
theStream_.open(fPath.c_str(),mode);
What does ''O_EXCL | O_CREAT'' expression doing in ''fstream::open''?
You are supposed to use constants from ''std::ios_base''...
I get the failure shown below. According to the man pages and
the standard, the second argument should be an int.
According to what standard? What page/clause/paragraph? My copy of the
standard states that the second argument has the type
''std::ios_base::openmode''.Thanks in advance for your help.
Mike.
--
g++ -I. -I../MdbUtil -c -o UniqueFile.o UniqueFile.cc
UniqueFile.cc: In member function `void MdbUtil::UniqueFile::open(constchar*,const char*, int, int, const char*)'':
UniqueFile.cc:64: invalid conversion from `int'' to`std::_Ios_Openmode'' UniqueFile.cc:64: initializing argument 2 of `void
std::basic_fstream<_CharT,_Traits>::open(const char*, std::_Ios_Openmode) [with _CharT =
char, _Traits= std::char_traits<char>]''
make: *** [UniqueFile.o] Error 1
Yes, I see my error now. My requirement is to open an ofstream,
and have it fail if the file already exists. I looked at the
constants in std::ios_base, and like the old fstream capability,
it does not appear to have the semantics to do this. If I am
correct about this, what is the best way to check for the
existence of a file?
(a) Please don''t top-post
(b) The only way I know in C++ to check if a file exists is to open
the file for reading [only] and check whether it succeeds. My
guess is that if it doesn''t succeed (there is no such file), then
you re-open the stream for writing and continue using it (if I
understood your intentions correctly).
Victor
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