Those listed here are supported by the latest C and C standards (both published in 2011), but those in yellow were introduced in C99 (only required for C implementations since C11), and may not be supported by libraries that comply with older standards. See also printf Print formatted data to stdout (function ) fscanf. Apr 14, 2004 fopen,fclose problem Forum: Bloodshed Software Forum. Creator: Nobody. I want to check if a file already exists, using fopen. This works, but after calling fopen on the file i cant delete the file until i close my program. I watched the handles that my program created, and everytime i use fopen to check if the file excists a new handle is. When append mode is used, the fopen fails. See z/OS XL C/C Programming Guide for more information about fopen default attributes. Samethread: This parameter specifies that I/O operations against the stream are restricted to the thread in which the stream was opened. The library will not lock the stream in a multithread environment. This is the unsigned integral type and is the result of the sizeof keyword. This macro is an integer, which represents the longest length of a char array suitable for holding the longest possible filename. If the implementation imposes no limit, then this value should be the recommended maximum. How to open files with fopen passed as a parameter. C / C Forums on Bytes.
-->Associates a stream with a file that was previously opened for low-level I/O.
Syntax
Parameters
fd
File descriptor of the open file.
mode
Type of file access.
Return Value
Each of these functions returns a pointer to the open stream. A null pointer value indicates an error. When an error occurs, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, errno is set either to EBADF, which indicates a bad file descriptor, or EINVAL, which indicates that mode was a null pointer.
For more information about these and other error codes, see _doserrno, errno, _sys_errlist, and _sys_nerr.
Remarks
The _fdopen function associates an I/O stream with the file that is identified by fd, and thus allows a file that is opened for low-level I/O to be buffered and formatted. _wfdopen is a wide-character version of _fdopen; the mode argument to _wfdopen is a wide-character string. _wfdopen and _fdopen otherwise behave identically.
Dec 11, 2019 To minimize the potential for errors, C has adopted the convention of using header files to contain declarations. You make the declarations in a header file, then use the #include directive in every.cpp file or other header file requires that declaration. The #include directive inserts a copy of the header file directly. Mar 25, 2011 ok,lets,here we use Dev C to make header file. 1) Open the Dev c and Create new Console application and save it in new folder. 2) Now,time to the Write a Code. Ok, When you Create new Project than main.cpp file create by default, in this file Write following codes. Header files in dev-C. Ask Question Asked 11 years ago. Active 2 years, 3 months ago. You need to put the #include after 'using namespace std;', in order to use your header file in the standard namespace. For me it is working. Share improve this answer. /how-to-use-header-files-in-dev-c.html.
File descriptors passed into _fdopen are owned by the returned FILE * stream. If _fdopen is successful, do not call _close on the file descriptor. Calling fclose on the returned FILE * also closes the file descriptor.
By default, this function's global state is scoped to the application. To change this, see Global state in the CRT.
Generic-Text Routine Mappings
| Tchar.h routine | _UNICODE and _MBCS not defined | _MBCS defined | _UNICODE defined |
|---|---|---|---|
| _tfdopen | _fdopen | _fdopen | _wfdopen |
The mode character string specifies the type of file access requested for the file:
| mode | Access |
|---|---|
| 'r' | Opens for reading. If the file does not exist or cannot be found, the fopen call fails. |
| 'w' | Opens an empty file for writing. If the given file exists, its contents are destroyed. |
| 'a' | Opens for writing at the end of the file (appending). Creates the file if it does not exist. |
| 'r+' | Opens for both reading and writing. The file must exist. |
| 'w+' | Opens an empty file for both reading and writing. If the file exists, its contents are destroyed. |
| 'a+' | Opens for reading and appending. Creates the file if it does not exist. |
When a file is opened with the 'a' or 'a+' access type, all write operations occur at the end of the file. The file pointer can be repositioned by using fseek or rewind, but it is always moved back to the end of the file before any write operation is carried out. Thus, existing data cannot be overwritten. When the 'r+', 'w+', or 'a+' access type is specified, both reading and writing are allowed (the file is said to be open for 'update'). However, when you switch between reading and writing, there must be an intervening fflush, fsetpos, fseek, or rewind operation. You can specify the current position for the fsetpos or fseek operation, if you want to.
In addition to the above values, the following characters can also be included in mode to specify the translation mode for newline characters:
| mode modifier | Behavior |
|---|---|
| t | Open in text (translated) mode. In this mode, carriage return-line feed (CR-LF) combinations are translated into one-line feeds (LF) on input, and LF characters are translated to CR-LF combinations on output. Also, Ctrl+Z is interpreted as an end-of-file character on input. |
| b | Open in binary (untranslated) mode. Any translations from t mode are suppressed. |
| c | Enable the commit flag for the associated filename so that the contents of the file buffer are written directly to disk if either fflush or _flushall is called. |
| n | Reset the commit flag for the associated filename to 'no-commit.' This is the default. It also overrides the global commit flag if you link your program with Commode.obj. The global commit flag default is 'no-commit' unless you explicitly link your program with Commode.obj. |
The t, c, and nmode options are Microsoft extensions for fopen and _fdopen. Do not use them if you want to preserve ANSI portability.
If t or b is not given in mode, the default translation mode is defined by the global variable _fmode. If t or b is prefixed to the argument, the function fails and returns NULL. For a discussion of text and binary modes, see Text and Binary Mode File I/O.
Valid characters for the mode string used in fopen and _fdopen correspond to oflag arguments used in _open and _sopen, as shown in this table:
| Characters in mode string | Equivalent oflag value for _open and _sopen |
|---|---|
| a | _O_WRONLY _O_APPEND (usually _O_WRONLY _O_CREAT _O_APPEND) |
| a+ | _O_RDWR _O_APPEND (usually _O_RDWR _O_APPEND _O_CREAT ) |
| r | _O_RDONLY |
| r+ | _O_RDWR |
| w | _O_WRONLY (usually _O_WRONLY _O_CREAT _O_TRUNC) |
| w+ | _O_RDWR (usually _O_RDWR _O_CREAT _O_TRUNC) |
| b | _O_BINARY |
| t | _O_TEXT |
| c | None |
| n | None |
Requirements
| Function | Required header |
|---|---|
| _fdopen | <stdio.h> |
| _wfdopen | <stdio.h> or <wchar.h> |
For more compatibility information, see Compatibility.
Dev C++ Opengl
Example
Input: crt_fdopen.txt
Output
See also
Stream I/O
_dup, _dup2
fclose, _fcloseall
fopen, _wfopen
freopen, _wfreopen
_open, _wopen
- The C Standard Library
- C Standard Library Resources
- C Programming Resources
- Selected Reading
The stdio.h header defines three variable types, several macros, and various functions for performing input and output.
Library Variables
Following are the variable types defined in the header stdio.h −
| Sr.No. | Variable & Description |
|---|---|
| 1 | size_t This is the unsigned integral type and is the result of the sizeof keyword. |
| 2 | FILE This is an object type suitable for storing information for a file stream. |
| 3 | fpos_t This is an object type suitable for storing any position in a file. |
Library Macros
Following are the macros defined in the header stdio.h −
| Sr.No. | Macro & Description |
|---|---|
| 1 | NULL This macro is the value of a null pointer constant. |
| 2 | _IOFBF, _IOLBF and _IONBF These are the macros which expand to integral constant expressions with distinct values and suitable for the use as third argument to the setvbuf function. |
| 3 | BUFSIZ This macro is an integer, which represents the size of the buffer used by the setbuf function. |
| 4 | EOF This macro is a negative integer, which indicates that the end-of-file has been reached. |
| 5 | FOPEN_MAX This macro is an integer, which represents the maximum number of files that the system can guarantee to be opened simultaneously. |
| 6 | FILENAME_MAX This macro is an integer, which represents the longest length of a char array suitable for holding the longest possible filename. If the implementation imposes no limit, then this value should be the recommended maximum value. |
| 7 | L_tmpnam This macro is an integer, which represents the longest length of a char array suitable for holding the longest possible temporary filename created by the tmpnam function. |
| 8 | SEEK_CUR, SEEK_END, and SEEK_SET These macros are used in the fseek function to locate different positions in a file. |
| 9 | TMP_MAX This macro is the maximum number of unique filenames that the function tmpnam can generate. |
| 10 | stderr, stdin, and stdout These macros are pointers to FILE types which correspond to the standard error, standard input, and standard output streams. |
Library Functions
Following are the functions defined in the header stdio.h −
Follow the same sequence of functions for better understanding and to make use of Try it(Online compiler) option, because file created in the first function will be used in subsequent functions.
| Sr.No. | Function & Description |
|---|---|
| 1 | int fclose(FILE *stream) Closes the stream. All buffers are flushed. |
| 2 | void clearerr(FILE *stream) Clears the end-of-file and error indicators for the given stream. |
| 3 | int feof(FILE *stream) Tests the end-of-file indicator for the given stream. |
| 4 | int ferror(FILE *stream) Tests the error indicator for the given stream. |
| 5 | int fflush(FILE *stream) Flushes the output buffer of a stream. |
| 6 | int fgetpos(FILE *stream, fpos_t *pos) Gets the current file position of the stream and writes it to pos. |
| 7 | FILE *fopen(const char *filename, const char *mode) Opens the filename pointed to by filename using the given mode. |
| 8 | size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream) Reads data from the given stream into the array pointed to by ptr. |
| 9 | FILE *freopen(const char *filename, const char *mode, FILE *stream) Associates a new filename with the given open stream and same time closing the old file in stream. |
| 10 | int fseek(FILE *stream, long int offset, int whence) Sets the file position of the stream to the given offset. The argument offset signifies the number of bytes to seek from the given whence position. |
| 11 | int fsetpos(FILE *stream, const fpos_t *pos) Sets the file position of the given stream to the given position. The argument pos is a position given by the function fgetpos. |
| 12 | long int ftell(FILE *stream) Returns the current file position of the given stream. |
| 13 | size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream) Writes data from the array pointed to by ptr to the given stream. |
| 14 | int remove(const char *filename) Deletes the given filename so that it is no longer accessible. |
| 15 | int rename(const char *old_filename, const char *new_filename) Causes the filename referred to, by old_filename to be changed to new_filename. |
| 16 | void rewind(FILE *stream) Sets the file position to the beginning of the file of the given stream. |
| 17 | void setbuf(FILE *stream, char *buffer) Defines how a stream should be buffered. |
| 18 | int setvbuf(FILE *stream, char *buffer, int mode, size_t size) Another function to define how a stream should be buffered. |
| 19 | FILE *tmpfile(void) Creates a temporary file in binary update mode (wb+). |
| 20 | char *tmpnam(char *str) Generates and returns a valid temporary filename which does not exist. |
| 21 | int fprintf(FILE *stream, const char *format, ..) Sends formatted output to a stream. |
| 22 | int printf(const char *format, ..) Sends formatted output to stdout. |
| 23 | int sprintf(char *str, const char *format, ..) Sends formatted output to a string. |
| 24 | int vfprintf(FILE *stream, const char *format, va_list arg) Sends formatted output to a stream using an argument list. |
| 25 | int vprintf(const char *format, va_list arg) Sends formatted output to stdout using an argument list. |
| 26 | int vsprintf(char *str, const char *format, va_list arg) Sends formatted output to a string using an argument list. |
| 27 | int fscanf(FILE *stream, const char *format, ..) Reads formatted input from a stream. |
| 28 | int scanf(const char *format, ..) Reads formatted input from stdin. |
| 29 | int sscanf(const char *str, const char *format, ..) Reads formatted input from a string. |
| 30 | int fgetc(FILE *stream) Gets the next character (an unsigned char) from the specified stream and advances the position indicator for the stream. |
| 31 | char *fgets(char *str, int n, FILE *stream) Reads a line from the specified stream and stores it into the string pointed to by str. It stops when either (n-1) characters are read, the newline character is read, or the end-of-file is reached, whichever comes first. |
| 32 | int fputc(int char, FILE *stream) Writes a character (an unsigned char) specified by the argument char to the specified stream and advances the position indicator for the stream. |
| 33 | int fputs(const char *str, FILE *stream) Writes a string to the specified stream up to but not including the null character. |
| 34 | int getc(FILE *stream) Gets the next character (an unsigned char) from the specified stream and advances the position indicator for the stream. |
| 35 | int getchar(void) Gets a character (an unsigned char) from stdin. |
| 36 | char *gets(char *str) Reads a line from stdin and stores it into the string pointed to by, str. It stops when either the newline character is read or when the end-of-file is reached, whichever comes first. |
| 37 | int putc(int char, FILE *stream) Writes a character (an unsigned char) specified by the argument char to the specified stream and advances the position indicator for the stream. |
| 38 | int putchar(int char) Writes a character (an unsigned char) specified by the argument char to stdout. |
| 39 | int puts(const char *str) Writes a string to stdout up to but not including the null character. A newline character is appended to the output. |
| 40 | int ungetc(int char, FILE *stream) Pushes the character char (an unsigned char) onto the specified stream so that the next character is read. |
| 41 | void perror(const char *str) Prints a descriptive error message to stderr. First the string str is printed followed by a colon and then a space. |