File I/O

These functions are declared in the main Allegro header file:

     #include <allegro5/allegro.h>

# ALLEGRO_FILE

    typedef struct ALLEGRO_FILE ALLEGRO_FILE;

Source Code

An opaque object representing an open file. This could be a real file on disk or a virtual file.

Examples:

- ex_file.c
- ex_dir.c
- ex_memfile.c

# ALLEGRO_FILE_INTERFACE

    typedef struct ALLEGRO_FILE_INTERFACE

Source Code

A structure containing function pointers to handle a type of “file”, real or virtual. See the full discussion in al_set_new_file_interface.

The fields are:

    void*         (*fi_fopen)(const char *path, const char *mode);
    bool          (*fi_fclose)(ALLEGRO_FILE *f);
    size_t        (*fi_fread)(ALLEGRO_FILE *f, void *ptr, size_t size);
    size_t        (*fi_fwrite)(ALLEGRO_FILE *f, const void *ptr, size_t size);
    bool          (*fi_fflush)(ALLEGRO_FILE *f);
    int64_t       (*fi_ftell)(ALLEGRO_FILE *f);
    bool          (*fi_fseek)(ALLEGRO_FILE *f, int64_t offset, int whence);
    bool          (*fi_feof)(ALLEGRO_FILE *f);
    int           (*fi_ferror)(ALLEGRO_FILE *f);
    const char *  (*fi_ferrmsg)(ALLEGRO_FILE *f);
    void          (*fi_fclearerr)(ALLEGRO_FILE *f);
    int           (*fi_fungetc)(ALLEGRO_FILE *f, int c);
    off_t         (*fi_fsize)(ALLEGRO_FILE *f);

The fi_open function must allocate memory for whatever userdata structure it needs. The pointer to that memory must be returned; it will then be associated with the file. The other functions can access that data by calling al_get_file_userdata on the file handle. If fi_open returns NULL then al_fopen will also return NULL.

The fi_fclose function must clean up and free the userdata, but Allegro will free the ALLEGRO_FILE handle.

If fi_fungetc is NULL, then Allegro’s default implementation of a 16 char long buffer will be used.

Examples:

- ex_curl.c

# ALLEGRO_SEEK

    typedef enum ALLEGRO_SEEK

Source Code

- ALLEGRO_SEEK_SET - seek relative to beginning of file
- ALLEGRO_SEEK_CUR - seek relative to current file position
- ALLEGRO_SEEK_END - seek relative to end of file

See also: al_fseek

Examples:

- ex_file.c
- ex_memfile.c
- ex_file_slice.c

# al_fopen

    ALLEGRO_FILE *al_fopen(const char *path, const char *mode)

Source Code

Creates and opens a file (real or virtual) given the path and mode. The current file interface is used to open the file.

Parameters:

- path - path to the file to open
- mode - access mode to open the file in (“r”, “w”, etc.)

Depending on the stream type and the mode string, files may be opened in “text” mode. The handling of newlines is particularly important. For example, using the default stdio-based streams on DOS and Windows platforms, where the native end-of-line terminators are CR+LF sequences, a call to al_fgetc may return just one character (‘\n’) where there were two bytes (CR+LF) in the file. When writing out ‘\n’, two bytes would be written instead. (As an aside, ‘\n’ is not defined to be equal to LF either.)

Newline translations can be useful for text files but is disastrous for binary files. To avoid this behaviour you need to open file streams in binary mode by using a mode argument containing a “b”, e.g. “rb”, “wb”.

Returns a file handle on success, or NULL on error.

See also: al_set_new_file_interface, al_fclose.

Examples:

- ex_file.c
- ex_file_slice.c
- ex_bitmap_file.c

# al_fopen_interface

    ALLEGRO_FILE *al_fopen_interface(const ALLEGRO_FILE_INTERFACE *drv,
       const char *path, const char *mode)

Source Code

Opens a file using the specified interface, instead of the interface set with al_set_new_file_interface.

See also: al_fopen

# al_fopen_slice

    ALLEGRO_FILE *al_fopen_slice(ALLEGRO_FILE *fp, size_t initial_size, const char *mode)

Source Code

Opens a slice (subset) of an already open random access file as if it were a stand alone file. While the slice is open, the parent file handle must not be used in any way.

The slice is opened at the current location of the parent file, up through `initial_size` bytes. The `initial_size` may be any non-negative integer that will not exceed the bounds of the parent file.

Seeking with `ALLEGRO_SEEK_SET` will be relative to this starting location. `ALLEGRO_SEEK_END` will be relative to the starting location plus the size of the slice.

The mode can be any combination of:

- r: read access
- w: write access
- e: expandable
- s: seek to the end of the slice upon [al_close] (this is the default behavior)
- n: disable the seeking behavior of “s”.

For example, a mode of “rw” indicates the file can be read and written. (Note that this is slightly different from the stdio modes.) Keep in mind that the parent file must support random access and be open in normal write mode (not append) for the slice to work in a well defined way.

If the slice is marked as expandable, then reads and writes can happen after the initial end point, and the slice will grow accordingly. Otherwise, all activity is restricted to the initial size of the slice.

A slice must be closed with al_fclose. The parent file will then be positioned immediately after the end of the slice. This behavior can be disabled by setting the “n” mode.

Since: 5.0.6, 5.1.0

See also: al_fopen

Examples:

- ex_file_slice.c

# al_fclose

    bool al_fclose(ALLEGRO_FILE *f)

Source Code

Close the given file, writing any buffered output data (if any).

Returns true on success, false on failure. errno is set to indicate the error.

Examples:

- ex_file.c
- ex_memfile.c
- ex_file_slice.c

# al_fread

    size_t al_fread(ALLEGRO_FILE *f, void *ptr, size_t size)

Source Code

Read ‘size’ bytes into the buffer pointed to by ‘ptr’, from the given file.

Returns the number of bytes actually read. If an error occurs, or the end-of-file is reached, the return value is a short byte count (or zero).

al_fread() does not distinguish between EOF and other errors. Use al_feof and al_ferror to determine which occurred.

See also: al_fgetc, al_fread16be, al_fread16le, al_fread32be, al_fread32le

Examples:

- ex_file.c
- ex_memfile.c
- ex_file_slice.c

# al_fwrite

    size_t al_fwrite(ALLEGRO_FILE *f, const void *ptr, size_t size)

Source Code

Write ‘size’ bytes from the buffer pointed to by ‘ptr’ into the given file.

Returns the number of bytes actually written. If an error occurs, the return value is a short byte count (or zero).

See also: al_fputc, al_fputs, al_fwrite16be, al_fwrite16le, al_fwrite32be, al_fwrite32le

Examples:

- ex_memfile.c
- ex_file_slice.c
- ex_synth.cpp

# al_fflush

    bool al_fflush(ALLEGRO_FILE *f)

Source Code

Flush any pending writes to the given file.

Returns true on success, false otherwise. errno is set to indicate the error.

See also: al_get_errno

# al_ftell

    int64_t al_ftell(ALLEGRO_FILE *f)

Source Code

Returns the current position in the given file, or -1 on error. errno is set to indicate the error.

On some platforms this function may not support large files.

See also: al_fseek, al_get_errno

Examples:

- ex_file.c
- ex_memfile.c

# al_fseek

    bool al_fseek(ALLEGRO_FILE *f, int64_t offset, int whence)

Source Code

Set the current position of the given file to a position relative to that specified by ‘whence’, plus ‘offset’ number of bytes.

‘whence’ can be:

- ALLEGRO_SEEK_SET - seek relative to beginning of file
- ALLEGRO_SEEK_CUR - seek relative to current file position
- ALLEGRO_SEEK_END - seek relative to end of file

Returns true on success, false on failure. errno is set to indicate the error.

After a successful seek, the end-of-file indicator is cleared and all pushback bytes are forgotten.

On some platforms this function may not support large files.

See also: al_ftell, al_get_errno

Examples:

- ex_file.c
- ex_memfile.c
- ex_file_slice.c

# al_feof

    bool al_feof(ALLEGRO_FILE *f)

Source Code

Returns true if the end-of-file indicator has been set on the file, i.e. we have attempted to read past the end of the file.

This does not return true if we simply are at the end of the file. The following code correctly reads two bytes, even when the file contains exactly two bytes:

    int b1 = al_fgetc(f);
    int b2 = al_fgetc(f);
    if (al_feof(f)) {
       /* At least one byte was unsuccessfully read. */
       report_error();
    }

See also: al_ferror, al_fclearerr

Examples:

- ex_file.c
- ex_memfile.c
- ex_file_slice.c

# al_ferror

    int al_ferror(ALLEGRO_FILE *f)

Source Code

Returns non-zero if the error indicator is set on the given file, i.e. there was some sort of previous error. The error code may be system or file interface specific.

See also: al_feof, al_fclearerr, al_ferrmsg

Examples:

- ex_file.c
- ex_record.c

# al_ferrmsg

    const char *al_ferrmsg(ALLEGRO_FILE *f)

Source Code

Return a message string with details about the last error that occurred on the given file handle. The returned string is empty if there was no error, or if the file interface does not provide more information.

See also: al_fclearerr, al_ferror

# al_fclearerr

    void al_fclearerr(ALLEGRO_FILE *f)

Source Code

Clear the error indicator for the given file.

The standard I/O backend also clears the end-of-file indicator, and other backends should try to do this. However, they may not if it would require too much effort (e.g. PhysicsFS backend), so your code should not rely on it if you need your code to be portable to other backends.

See also: al_ferror, al_feof

# al_fungetc

    int al_fungetc(ALLEGRO_FILE *f, int c)

Source Code

Ungets a single byte from a file. Pushed-back bytes are not written to the file, only made available for subsequent reads, in reverse order.

The number of pushbacks depends on the backend. The standard I/O backend only guarantees a single pushback; this depends on the libc implementation.

For backends that follow the standard behavior, the pushback buffer will be cleared after any seeking or writing; also calls to al_fseek and al_ftell are relative to the number of pushbacks. If a pushback causes the position to become negative, the behavior of al_fseek and al_ftell are undefined.

See also: al_fgetc, al_get_errno

Examples:

- ex_file.c
- ex_memfile.c

# al_fsize

    int64_t al_fsize(ALLEGRO_FILE *f)

Source Code

Return the size of the file, if it can be determined, or -1 otherwise.

Examples:

- ex_file.c
- ex_file_slice.c

# al_fgetc

    int al_fgetc(ALLEGRO_FILE *f)

Source Code

Read and return next byte in the given file. Returns EOF on end of file or if an error occurred.

See also: al_fungetc

Examples:

- ex_file.c
- ex_memfile.c
- ex_curl.c

# al_fputc

    int al_fputc(ALLEGRO_FILE *f, int c)

Source Code

Write a single byte to the given file. The byte written is the value of c cast to an unsigned char.

Parameters:

- c - byte value to write
- f - file to write to

Returns the written byte (cast back to an int) on success, or EOF on error.

# al_fprintf

    int al_fprintf(ALLEGRO_FILE *pfile, const char *format, ...)

Source Code

Writes to a file with stdio “printf”-like formatting. Returns the number of bytes written, or a negative number on error.

See also: al_vfprintf

# al_vfprintf

    int al_vfprintf(ALLEGRO_FILE *pfile, const char *format, va_list args)

Source Code

Like al_fprintf but takes a va_list. Useful for creating your own variations of formatted printing. Returns the number of bytes written, or a negative number on error.

See also: al_fprintf

# al_fread16le

    int16_t al_fread16le(ALLEGRO_FILE *f)

Source Code

Reads a 16-bit word in little-endian format (LSB first).

On success, returns the 16-bit word. On failure, returns EOF (-1). Since -1 is also a valid return value, use al_feof to check if the end of the file was reached prematurely, or al_ferror to check if an error occurred.

See also: al_fread16be

# al_fread16be

    int16_t al_fread16be(ALLEGRO_FILE *f)

Source Code

Reads a 16-bit word in big-endian format (MSB first).

On success, returns the 16-bit word. On failure, returns EOF (-1). Since -1 is also a valid return value, use al_feof to check if the end of the file was reached prematurely, or al_ferror to check if an error occurred.

See also: al_fread16le

# al_fwrite16le

    size_t al_fwrite16le(ALLEGRO_FILE *f, int16_t w)

Source Code

Writes a 16-bit word in little-endian format (LSB first).

Returns the number of bytes written: 2 on success, less than 2 on an error.

See also: al_fwrite16be

# al_fwrite16be

    size_t al_fwrite16be(ALLEGRO_FILE *f, int16_t w)

Source Code

Writes a 16-bit word in big-endian format (MSB first).

Returns the number of bytes written: 2 on success, less than 2 on an error.

See also: al_fwrite16le

# al_fread32le

    int32_t al_fread32le(ALLEGRO_FILE *f)

Source Code

Reads a 32-bit word in little-endian format (LSB first).

On success, returns the 32-bit word. On failure, returns EOF (-1). Since -1 is also a valid return value, use al_feof to check if the end of the file was reached prematurely, or al_ferror to check if an error occurred.

See also: al_fread32be

Examples:

- ex_memfile.c
- ex_file_slice.c

# al_fread32be

    int32_t al_fread32be(ALLEGRO_FILE *f)

Source Code

Read a 32-bit word in big-endian format (MSB first).

On success, returns the 32-bit word. On failure, returns EOF (-1). Since -1 is also a valid return value, use al_feof to check if the end of the file was reached prematurely, or al_ferror to check if an error occurred.

See also: al_fread32le

# al_fwrite32le

    size_t al_fwrite32le(ALLEGRO_FILE *f, int32_t l)

Source Code

Writes a 32-bit word in little-endian format (LSB first).

Returns the number of bytes written: 4 on success, less than 4 on an error.

See also: al_fwrite32be

Examples:

- ex_memfile.c
- ex_file_slice.c

# al_fwrite32be

    size_t al_fwrite32be(ALLEGRO_FILE *f, int32_t l)

Source Code

Writes a 32-bit word in big-endian format (MSB first).

Returns the number of bytes written: 4 on success, less than 4 on an error.

See also: al_fwrite32le

# al_fgets

    char *al_fgets(ALLEGRO_FILE *f, char * const buf, size_t max)

Source Code

Read a string of bytes terminated with a newline or end-of-file into the buffer given. The line terminator(s), if any, are included in the returned string. A maximum of max-1 bytes are read, with one byte being reserved for a NUL terminator.

Parameters:

- f - file to read from
- buf - buffer to fill
- max - maximum size of buffer

Returns the pointer to buf on success. Returns NULL if an error occurred or if the end of file was reached without reading any bytes.

See al_fopen about translations of end-of-line characters.

See also: al_fget_ustr

Examples:

- ex_memfile.c
- ex_file_slice.c

# al_fget_ustr

    ALLEGRO_USTR *al_fget_ustr(ALLEGRO_FILE *f)

Source Code

Read a string of bytes terminated with a newline or end-of-file. The line terminator(s), if any, are included in the returned string.

On success returns a pointer to a new ALLEGRO_USTR structure. This must be freed eventually with al_ustr_free. Returns NULL if an error occurred or if the end of file was reached without reading any bytes.

See al_fopen about translations of end-of-line characters.

See also: al_fgetc, al_fgets

# al_fputs

    int al_fputs(ALLEGRO_FILE *f, char const *p)

Source Code

Writes a string to file. Apart from the return value, this is equivalent to:

    al_fwrite(f, p, strlen(p));

Parameters:

- f - file handle to write to
- p - string to write

Returns a non-negative integer on success, EOF on error.

Note: depending on the stream type and the mode passed to al_fopen, newline characters in the string may or may not be automatically translated to native end-of-line sequences, e.g. CR/LF instead of LF.

See also: al_fwrite

Examples:

- ex_memfile.c

# Standard I/O specific routines

## al_fopen_fd

    ALLEGRO_FILE *al_fopen_fd(int fd, const char *mode)

Source Code

Create an ALLEGRO_FILE object that operates on an open file descriptor using stdio routines. See the documentation of fdopen() for a description of the ‘mode’ argument.

Returns an ALLEGRO_FILE object on success or NULL on an error. On an error, the Allegro errno will be set and the file descriptor will not be closed.

The file descriptor will be closed by al_fclose so you should not call close() on it.

See also: al_fopen

## al_make_temp_file

    ALLEGRO_FILE *al_make_temp_file(const char *template, ALLEGRO_PATH **ret_path)

Source Code

Make a temporary randomly named file given a filename ‘template’.

‘template’ is a string giving the format of the generated filename and should include one or more capital Xs. The Xs are replaced with random alphanumeric characters, produced using a simple pseudo-random number generator only. There should be no path separators.

If ‘ret_path’ is not NULL, the address it points to will be set to point to a new path structure with the name of the temporary file.

Returns the opened ALLEGRO_FILE on success, NULL on failure.

Examples:

- ex_file_slice.c
- ex_record.c

# Alternative file streams

By default, the Allegro file I/O routines use the C library I/O routines, hence work with files on the local filesystem, but can be overridden so that you can read and write to other streams. For example, you can work with blocks of memory or sub-files inside .zip files.

There are two ways to get an ALLEGRO_FILE that doesn’t use stdio. An addon library may provide a function that returns a new ALLEGRO_FILE directly, after which, all al_f* calls on that object will use overridden functions for that type of stream. Alternatively, al_set_new_file_interface changes which function will handle the following al_fopen calls for the current thread.

## al_set_new_file_interface

    void al_set_new_file_interface(const ALLEGRO_FILE_INTERFACE *file_interface)

Source Code

Set the ALLEGRO_FILE_INTERFACE table for the calling thread. This will change the handler for later calls to al_fopen.

See also: al_set_standard_file_interface, al_store_state, al_restore_state.

Examples:

- ex_curl.c

## al_set_standard_file_interface

    void al_set_standard_file_interface(void)

Source Code

Set the ALLEGRO_FILE_INTERFACE table to the default, for the calling thread. This will change the handler for later calls to al_fopen.

See also: al_set_new_file_interface

Examples:

- ex_android.c

## al_get_new_file_interface

    const ALLEGRO_FILE_INTERFACE *al_get_new_file_interface(void)

Source Code

Return a pointer to the ALLEGRO_FILE_INTERFACE table in effect for the calling thread.

See also: al_store_state, al_restore_state.

## al_create_file_handle

    ALLEGRO_FILE *al_create_file_handle(const ALLEGRO_FILE_INTERFACE *drv,
       void *userdata)

Source Code

Creates an empty, opened file handle with some abstract user data. This allows custom interfaces to extend the ALLEGRO_FILE struct with their own data. You should close the handle with the standard al_fclose function when you are finished with it.

See also: al_fopen, al_fclose, al_set_new_file_interface

## al_get_file_userdata

    void *al_get_file_userdata(ALLEGRO_FILE *f)

Source Code

Returns a pointer to the custom userdata that is attached to the file handle. This is intended to be used by functions that extend ALLEGRO_FILE_INTERFACE.

Examples:

- ex_curl.c

Allegro version 5.2.10 - Last updated: 2024-12-29 03:54:49 UTC