std::fopen

Defined in header <cstdio>	?	?
std::FILE* fopen( const char* filename, const char* mode );	?	?

打开由filename并返回与该文件关联的文件流。mode用于确定文件访问模式。

参数

filename	-	file name to associate the file stream to
mode	-	null-terminated character string determining file access mode File access mode string Meaning Explanation Action if file already exists Action if file does not exist "r" read Open a file for reading read from start failure to open "w" write Create a file for writing destroy contents create new "a" append Append to a file write to end create new "r+" read extended Open a file for read/write read from start error "w+" write extended Create a file for read/write destroy contents create new "a+" append extended Open a file for read/write write to end create new File access mode flag "b" can optionally be specified to open a file in binary mode. This flag has no effect on POSIX systems, but on Windows, for example, it disables special handling of '\n' and '\x1A'. On the append file access modes, data is written to the end of the file regardless of the current position of the file position indicator.	File access mode string	Meaning	Explanation	Action if file already exists	Action if file does not exist	"r"	read	Open a file for reading	read from start	failure to open	"w"	write	Create a file for writing	destroy contents	create new	"a"	append	Append to a file	write to end	create new	"r+"	read extended	Open a file for read/write	read from start	error	"w+"	write extended	Create a file for read/write	destroy contents	create new	"a+"	append extended	Open a file for read/write	write to end	create new	File access mode flag "b" can optionally be specified to open a file in binary mode. This flag has no effect on POSIX systems, but on Windows, for example, it disables special handling of '\n' and '\x1A'. On the append file access modes, data is written to the end of the file regardless of the current position of the file position indicator.
File access mode string	Meaning	Explanation	Action if file already exists	Action if file does not exist
"r"	read	Open a file for reading	read from start	failure to open
"w"	write	Create a file for writing	destroy contents	create new
"a"	append	Append to a file	write to end	create new
"r+"	read extended	Open a file for read/write	read from start	error
"w+"	write extended	Create a file for read/write	destroy contents	create new
"a+"	append extended	Open a file for read/write	write to end	create new

可以选择指定文件访问模式标志“b”以二进制模式打开文件。此标志对POSIX系统没有影响，但在Windows上，它禁用%27\n%27和%27\x1A%27的特殊处理。在附加文件访问模式上，数据被写入文件的末尾，而不管文件位置指示符的当前位置。

返回值

如果成功，则返回指向控制打开的文件流的对象的指针，清除eof和Error位。除非文件名引用交互设备，否则流将被完全缓冲。

如果出现错误，则返回一个空指针。POSIX要求那errno在这种情况下。

注记

格式filename是实现定义的，不一定引用文件%28例如。它可能是通过文件系统API%29访问的控制台或其他设备。在支持他们的平台上，filename可以包括绝对或相对的文件系统路径。

有关可移植目录和文件命名，请参见C++文件系统库或加油。文件系统...

例

二次

#include <cstdio>
#include <cstdlib>
 
int main()
{
    FILE* fp = std::fopen("test.txt", "r");
    if(!fp) {
        std::perror("File opening failed");
        return EXIT_FAILURE;
    }
 
    int c; // note: int, not char, required to handle EOF
    while ((c = std::fgetc(fp)) != EOF) { // standard C I/O file reading loop
       std::putchar(c);
    }
 
    if (std::ferror(fp))
        std::puts("I/O error when reading");
    else if (std::feof(fp))
        std::puts("End of file reached successfully");
 
    std::fclose(fp);
}

二次

另见

fclose	closes a file (function)
fflush	synchronizes an output stream with the actual file (function)
freopen	open an existing stream with a different name (function)

c fopen文件

 ? cppreference.com

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http：//en.cppreference.com/w/cpp/io/c/fopen

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最后更新于：2017-12-18