f_open

The f_open function creates or opens the file and initialize a file object structure to be used to access the file.

FRESULT f_open (
  FIL* FileObject,      // Pointer to the file object structure
  const char* FileName, // Pointer to the file neme
  BYTE ModeFlags        // Mode flags
);

Parameters

FileObject

Pointer to the blank file object structure to be initialized. After the f_open() succeeded, the file can be accessed with the file object structure until it is closed.

FileName

Pointer to a null-terminated string specifies the full-path file name to create or open. The directory separator is '/'. Because the FatFs module does not have a concept of current directory, a full-path name that followed from the root directory must be used. Leading space charactors are skipped if exist, and heading '/' can be exist or omitted.

ModeFlags

Specifies the type of access and open method for the file. It is specified by a combination of following flags.

Value	Description
FA_READ	Specifies read access to the object. Data can be read from the file. Combine with FA_WRITE for read-write access.
FA_WRITE	Specifies write access to the object. Data can be written to the file. Combine with FA_READ for read-write access.
FA_OPEN_EXISTING	Opens the file. The function fails if the file is not existing.
FA_CREATE_ALWAYS	Creates a new file. If the file is existing, it is truncated and overwritten.
FA_OPEN_ALWAYS	Opens the file, if it is existing. If not, the function creates the new file.

Return Values

FR_OK (0)

The function succeeded. The FileObject structure is used for subsequent calls to refer to the file. When close the file, use function f_close().

FR_NO_FILE

Could not find the file.

FR_NO_PATH

Could not find the path.

FR_INVALID_NAME

The file name is invalid.

FR_DENIED

The required access was denied due to any of following reasons: write mode open of a file that has read-only attribute, file creation under existing a same name directory or read-only file, cannot be created due to the directory table or disk full.

FR_NOT_READY

The disk drive cannot work due to no medium in the drive or any other reason.

FR_WRITE_PROTECTED

Write mode open or creation under the medium is write protected.

FR_RW_ERROR

Any error occured in low level disk I/O.

FR_INCORRECT_DISK_CHANGE

Incorrect disk removal/change has occured.

FR_NOT_ENABLED

FatFs module is not enabled.

FR_NO_FILESYSTEM

There is no valid FAT partition on the disk.

Description

To start FatFs module, prepare a work area (FATFS structure), fill it with zero and set its address to the global variable FatFs to give the work area to the FatFs module. All file functions can work after the initialization. f_mountdrv() can also be used instead of the zero filling, however, the physical drive must be ready at that time. To terminate use of the FatFs module, close all files, clear FatFs and then the work area can be discarded.

Flags FA_WRITE, FA_CREATE_ALWAYS, FA_OPEN_ALWAYS are not supported in read-only configuration.

Example (File Copy)

void main ()
{
    FATFS fs;            // FatFs work area
    FIL fsrc, fdst;      // file structures
    BYTE buffer[4096];   // file copy buffer
    FRESULT res;         // FatFs function common result code
    WORD br, bw;         // File R/W count


    // Give a work area to FatFs module (activate FatFs module)
    FatFs = &fs;
    memset(&fs, 0, sizeof(FATFS));  // Clear work area. f_mountdrv() can also be used instead.

    // Open source file
    res = f_open(&fsrc, "srcfile.dat", FA_OPEN_EXISTING | FA_READ);
    if (res) die(res);

    // Create destination file
    res = f_open(&fdst, "dstfile.dat", FA_CREATE_ALWAYS | FA_WRITE);
    if (res) die(res);

    // Copy source to destination
    for (;;) {
        res = f_read(&fsrc, buffer, sizeof(buffer), &br);
        if (res || br == 0) break;   // error or eof
        res = f_write(&fdst, buffer, br, &bw);
        if (res || bw < br) break;   // error or disk full
    }

    // Close all files
    f_close(&fsrc);
    f_close(&fdst);

    // Deactivate FatFs module
    FatFs = NULL;
}

References

f_read, f_write, f_close, FIL, FATFS