fopen返回NULL - 哪里是导致错误的列表？ [英] NULL returned by fopen - where is a list of what's causing the error?
问题描述
我正在尝试打开附加文件。即。如果文件存在，打开
它是否可以附加，如果没有，则创建它。我回来了一个NULL指针，
，不知道为什么。这是我的代码：
FILE * pFile;
char * cFileName;
cFileName = argv [++ i];
pFile = fopen（cFileName，" a +"）;
cFileName有一个有效的文件名（''apm.dbg''），并且我已经在目录中完整地写了
权限。我可以进入fopen，当打开文件
时，我可以在另一个窗口中看到该文件是使用
零字节创建的。然而，pFile返回为NULL。
是否有一个函数调用我可以告诉它实际上是什么错误？
ferrad写道：我正在尝试打开一个文件进行追加。即。如果文件存在，打开
它是否附加，如果没有，则创建它。我正在找回一个NULL指针，
并且不知道为什么。这是我的代码：
FILE * pFile;
char * cFileName;
cFileName = argv [++ i];
pFile = fopen（cFileName，"一个+ QUOT）;
您的代码不可编辑/可运行。例如。什么是''我'？
cFileName有一个有效的文件名（''apm.dbg''），我在目录中有完整的写权限。我可以进入fopen，当打开文件
时，我可以在另一个窗口中看到该文件是用零字节创建的。但是pFile返回为NULL。
是否有函数调用我可以告诉它实际上是什么错误？
AFAIK， standard仅指定fopen（）在因任何原因失败时返回NULL
：
7.19.5.3.8
fopen函数返回一个指向控制流的对象的指针。如果打开操作失败，fopen返回一个空的
指针。
干杯
弗拉基米尔
-
我的电子邮件地址是真的，我看了。
" ferrad" <交流*** @ hotmail.com>在消息中写道
news：11 ********************* @ g14g2000cwa.googlegro ups.com ...我正在尝试打开一个文件进行追加。即。如果文件存在，打开
它是否附加，如果没有，则创建它。我正在找回一个NULL指针，
并且不知道为什么。这是我的代码：
FILE * pFile;
char * cFileName;
cFileName = argv [++ i];
pFile = fopen（cFileName，" a +"）;
cFileName有一个有效的文件名（''apm.dbg''），我在目录中有完整的写权限。我可以进入fopen，当打开文件
时，我可以在另一个窗口中看到该文件是用零字节创建的。但是pFile返回为NULL。
是否有函数调用我可以告诉它实际上是什么错误？
唯一的事情标准C表示返回值
''fopen（）''如果
文件的打开失败则为NULL，如果失败则为非NULL它成功了。
失败的任何特殊原因都将取决于平台。
您应该查阅您的编译器和/或平台文档
（例如，对于错误代码列表，它会提供更多
特定信息）。许多实现为此目的提供了扩展
。
-Mike
ferrad写道：我正在尝试打开一个文件进行追加。即。如果文件存在，打开
它是否附加，如果没有，则创建它。我正在找回一个NULL指针，
并且不知道为什么。这是我的代码：
FILE * pFile;
char * cFileName;
cFileName = argv [++ i];
pFile = fopen（cFileName，" a +"）;
cFileName有一个有效的文件名（''apm.dbg''），我在目录中有完整的写权限。我可以进入fopen，当打开文件
时，我可以在另一个窗口中看到该文件是用零字节创建的。但是pFile返回为NULL。
是否有一个函数调用我可以告诉它实际上是什么错误？
如果你包含string.h和errno.h你可以使用strerror（errno）获取
a字符串来解释错误。
-
Ioan - Ciprian Tandau
tandau _at_ freeshell _dot_ org（希望现在还不算太晚）
（......它仍然有效......）
I am trying to open a file for appending. ie. if the file exists, open
it for appending, if not, create it. I am getting back a NULL pointer,
and do not know why. Here is my code:
FILE *pFile;
char *cFileName;
cFileName=argv[++i];
pFile = fopen(cFileName,"a+");
cFileName has a valid filename (''apm.dbg''), and I have full write
permissions in the directory. I can step into fopen and when the file
is opened, I can see in another window that the file is created with
zero bytes. However pFile is returned as NULL.
Is there a function call I can make to tell what the error actually is?
ferrad wrote:I am trying to open a file for appending. ie. if the file exists, open
it for appending, if not, create it. I am getting back a NULL pointer,
and do not know why. Here is my code:
FILE *pFile;
char *cFileName;
cFileName=argv[++i];
pFile = fopen(cFileName,"a+");
Your code is not compilable/runnable. E.g. what is ''i''?
cFileName has a valid filename (''apm.dbg''), and I have full write
permissions in the directory. I can step into fopen and when the file
is opened, I can see in another window that the file is created with
zero bytes. However pFile is returned as NULL.
Is there a function call I can make to tell what the error actually is?
AFAIK, the standard only specifies that fopen() returns NULL
when it fails for whatever reason:
7.19.5.3.8
The fopen function returns a pointer to the object controlling
the stream. If the open operation fails, fopen returns a null
pointer.
Cheers
Vladimir
--
My e-mail address is real, and I read it.
"ferrad" <ac***@hotmail.com> wrote in message
news:11*********************@g14g2000cwa.googlegro ups.com...I am trying to open a file for appending. ie. if the file exists, open
it for appending, if not, create it. I am getting back a NULL pointer,
and do not know why. Here is my code:
FILE *pFile;
char *cFileName;
cFileName=argv[++i];
pFile = fopen(cFileName,"a+");
cFileName has a valid filename (''apm.dbg''), and I have full write
permissions in the directory. I can step into fopen and when the file
is opened, I can see in another window that the file is created with
zero bytes. However pFile is returned as NULL.
Is there a function call I can make to tell what the error actually is?
The only thing standard C says about the return value of
''fopen()'' is that it will be NULL if the opening of the
file failed, and non-NULL if it succeeded.
Any particular reasons for failure will be platform-dependent.
You should consult your compiler and/or platform documentation
(e.g. for a list of ''error codes'' which would give more
specific information). Many implementations provide extensions
for this very purpose.
-Mike
ferrad wrote:I am trying to open a file for appending. ie. if the file exists, open
it for appending, if not, create it. I am getting back a NULL pointer,
and do not know why. Here is my code:
FILE *pFile;
char *cFileName;
cFileName=argv[++i];
pFile = fopen(cFileName,"a+");
cFileName has a valid filename (''apm.dbg''), and I have full write
permissions in the directory. I can step into fopen and when the file
is opened, I can see in another window that the file is created with
zero bytes. However pFile is returned as NULL.
Is there a function call I can make to tell what the error actually is?
If you include string.h and errno.h you could use strerror(errno) to obtain
a string explaining the error.
--
Ioan - Ciprian Tandau
tandau _at_ freeshell _dot_ org (hope it''s not too late)
(... and that it still works...)
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