cfopen⽂件读写
fopen 创建文件fopen
<cstdio>
FILE * fopen ( const char * filename, const char * mode );
Open file
Opens the file whose name is specified in the parameter filename and associates it with a stream that can be identified in future operations by the FILE object whose pointer is returned. The operations that are allowed on the stream and how these are performed are defined by the mode parameter.
The running environment supports at least FOPEN_MAX files open simultaneously; FOPEN_MAX is a macro constant defined in <cstdio>.
Parameters
filename
C string containing the name of the file to be opened. This paramenter must follow the file name specifications of the running
environment and can include a path if the system supports it.
mode
C string containing a file access modes. It can be:
"r"Open a file for reading. The file must exist.
"w"Create an empty file for writing. If a file with the same name already exists its content is erased and the file is treated as a new empty file.
"a"Append to a file. Writing operations append data at the end of the file. The file is created if it does not exist. "r+"Open a file for update both reading and writing. The file must exist.
"w+"Create an empty file for both reading and writing. If a file with the same name already exists its content is erased and the file is treated as a new empty file.
"a+"Open a file for reading and appending. All writing operations are performed at the end of the file, protecting the previous content to be overwritten. You can reposition (, ) the internal pointer to anywhere in the file for reading, but writing operations will move it back to the end of file. The file is created if it does not exist.
With the mode specifiers above the file is open as a text file. In order to open a file as a binary file, a "b" character has to be included in
the mode string. This additional "b" character can either be appended at the end of the string (thus making the following compound modes: "rb", "wb", "ab", "r+b", "w+b", "a+b") or be inserted between the letter and the "+" sign for the mixed modes ("rb+", "wb+", "ab+"). Additional characters may follow the sequence, although they should have no effect. For example, "t" is sometimes appended to make explicit the file is a text file.
In the case of text files, depending on the environment where the application runs, some special character conversion may occur in
input/output operations to adapt them to a system-specific text file format. In many environments, such as most UNIX-based systems, it makes no difference to open a file as a text file or a binary file; Both ar
e treated exactly the same way, but differentiation is recommended for a better portability.
For the modes where both read and writing (or appending) are allowed (those which include a "+" sign), the stream should be flushed () or repositioned (, , ) between either a reading operation followed by a writing operation or a writing operation followed by a reading operation. Return Value
If the file has been successfully opened the function will return a pointer to a  object that is used to identify the stream on all further operations involving it. Otherwise, a null pointer is returned.
Example
1
2 3 4 5 6 7 8 9 10 11 12 13/* fopen example */ #include <stdio.h> int main () {
FILE * pFile; pFile = fopen ("","w");
if (pFile!=NULL)
{
fputs ("fopen example",pFile);
fclose (pFile);
}
return 0;
}
fopen ( string filename, string mode ）
返回值是 FILE*
fopen() 中的 mode 的可能值列表
mode说明
'r'只读⽅式打开，将⽂件指针指向⽂件头。
'r+'读写⽅式打开，将⽂件指针指向⽂件头。
'w'写⼊⽅式打开，将⽂件指针指向⽂件头并将⽂件⼤⼩截为零。如果⽂件不存在则尝试创建之。'w+'读写⽅式打开，将⽂件指针指向⽂件头并将⽂件⼤⼩截为零。如果⽂件不存在则尝试创建之。'a'写⼊⽅式打开，将⽂件指针指向⽂件末尾。如果⽂件不存在则尝试创建之。
'a+'读写⽅式打开，将⽂件指针指向⽂件末尾。如果⽂件不存在则尝试创建之。
'x'创建并以写⼊⽅式打开，将⽂件指针指向⽂件头。如果⽂件已存在，则 fopen() 调⽤失败并返回 FALSE，并⽣成⼀条 E_WARNING 级别的错误信息。如果⽂件不存在则尝试创建之。这和给底层的 open(2) 系统调⽤指定 O_EXCL|O_CREAT 标记是等价的。此选项被 PHP 4.3.2 以及以后的版本所⽀持，仅能⽤于本地⽂件。
'x+'创建并以读写⽅式打开，将⽂件指针指向⽂件头。如果⽂件已存在，则 fopen() 调⽤失败并返回 FALSE，并⽣成⼀条 E_WARNING 级别的错误信息。如果⽂件不存在则尝试创建之。这和给底层的 open(2) 系统调⽤指定 O_EXCL|O_CREAT 标记是等价的。此选项被 PHP 4.3.2 以及以后的版本所⽀持，仅能⽤于本地⽂件。
在操作⼆进制⽂件时如果没有指定'b'标记，可能会碰到⼀些奇怪的问题，包括坏掉的图⽚⽂件以及关于\r\n字符的奇怪问题。为移植性考虑，强烈建议在⽤ fopen() 打开⽂件时总是使⽤ 'b' 标记。

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