| I/O manipulators | ||||
| Print functions(C++23) | ||||
| C-style I/O | ||||
| Buffers | ||||
(C++23) | ||||
(C++98/26*) | ||||
(C++20) | ||||
| Streams | ||||
| Abstractions | ||||
| File I/O | ||||
| String I/O | ||||
| Array I/O | ||||
(C++23) | ||||
(C++23) | ||||
(C++23) | ||||
(C++98/26*) | ||||
(C++98/26*) | ||||
(C++98/26*) | ||||
| Synchronized Output | ||||
(C++20) | ||||
| Types | ||||
| Error category interface | ||||
(C++11) | ||||
(C++11) |
| Types and objects | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Defined in header <cstdio> | ||
std::FILE* fopen(constchar* filename,constchar* mode); | ||
Opens a file indicated byfilename and returns a file stream associated with that file.mode is used to determine the file access mode.
Contents |
| filename | - | file name to associate the file stream to |
| mode | - | null-terminated character string determiningfile 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 | returnNULL and set error |
| "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 | returnNULL and set 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 filein 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 flag"x" can optionally be appended to"w" or"w+" specifiers. This flag forces the function to fail if the file exists, instead of overwriting it.(C++17) | ||||
| The behavior is undefined if the mode is not one of the strings listed above. Some implementations define additional supported modes (e.g.Windows). | ||||
If successful, returns a pointer to the object that controls the opened file stream, with both eof and error bits cleared. The stream is fully buffered unlessfilename refers to an interactive device.
On error, returns a null pointer.POSIX requires thaterrno is set in this case.
The format offilename is implementation-defined, and does not necessarily refer to a file (e.g. it may be the console or another device accessible through filesystem API). On platforms that support them,filename may include absolute or relative filesystem path.
For portable directory and file naming, seeC++ filesystem library orboost.filesystem.
#include <cstdio>#include <cstdlib> int main(){int is_ok=EXIT_FAILURE; FILE* fp= std::fopen("/tmp/test.txt","w+");if(!fp){std::perror("File opening failed");return is_ok;} int c;// Note: int, not char, required to handle EOFwhile((c=std::fgetc(fp))!=EOF)// Standard C I/O file reading loopstd::putchar(c); if(std::ferror(fp))std::puts("I/O error when reading");elseif(std::feof(fp)){std::puts("End of file reached successfully"); is_ok=EXIT_SUCCESS;} std::fclose(fp);return is_ok;}
Output:
End of file reached successfully
| closes a file (function)[edit] | |
| synchronizes an output stream with the actual file (function)[edit] | |
| open an existing stream with a different name (function)[edit] | |
C documentation forfopen | |
