FUNCTION_BLOCK ExampleSystemOpen
    VAR
        data : ARRAY[0..63] OF BYTE;
        fd : DINT := -1;
        flagsWriteAppend : DINT := -1;
        flagsCreateTruncWrite : DINT := -1;
        mode : DINT := -1;
        path : STRING[64];
        didOpen : BOOL;
        writeOk : BOOL;
    END_VAR
    
    VAR CONSTANT
        /* Append new information to the end of the file. */
        Windows_O_APPEND : DINT := 8;
        /* If the file does not exist, create it. If the O_CREAT option is used, then you must include the third parameter (). */
        Windows_O_CREAT  : DINT := 256;
        /* Combined with the O_CREAT option, it ensures that the caller must create the file. If the file already exists, the call will fail. */
        Windows_O_EXCL   : DINT := 1024;
        /* Open the file so that it is read only. */
        Windows_O_RDONLY : DINT := 0;
        /* Open the file so that it can be read from and written to. */
        Windows_O_RDWR   : DINT := 2;
        /* Initially clear all data from the file. */
        Windows_O_TRUNC  : DINT := 512;
        /* Open the file so that it is write only. */
        Windows_O_WRONLY : DINT := 1;
        
        /* Only reading permitted. */
        Windows_S_IREAD : DINT := 256;
        /* Writing permitted. (In effect, permits reading and writing.) */
        Windows_S_IWRITE : DINT := 128;
        
        /* Append new information to the end of the file. */
        Linux_O_APPEND : DINT := 8;
        /* If the file does not exist, create it. If the O_CREAT option is used, then you must include the third parameter (mode). */
        Linux_O_CREAT  : DINT := 512;
        /* Combined with the O_CREAT option, it ensures that the caller must create the file. If the file already exists, the call will fail. */
        Linux_O_EXCL   : DINT := 2048;
        /* Open the file so that it is read only. */
        Linux_O_RDONLY : DINT := 0;
        /* Open the file so that it can be read from and written to. */
        Linux_O_RDWR   : DINT := 2;
        /* Initially clear all data from the file. */
        Linux_O_TRUNC  : DINT := 1024;
        /* Open the file so that it is write only. */
        Linux_O_WRONLY : DINT := 1;
    END_VAR
    
    IF isTargetWinX86() THEN
        path := 'c:\tmp\log.dat';
        /* write access, append to file content */
        flagsWriteAppend := IOR(Windows_O_WRONLY, Windows_O_APPEND);
        /* write access, create file and truncate file to length 0 */
        flagsCreateTruncWrite := IOR(Windows_O_WRONLY, Windows_O_CREAT, Windows_O_TRUNC);
        /* read and write access for the user */
        mode := IOR(Windows_S_IREAD, Windows_S_IWRITE);
    END_IF;
    
    IF isTargetLinuxX86() THEN
        path := '/tmp/log.dat';
        /* write access, append to file content */
        flagsWriteAppend := IOR(Linux_O_WRONLY, Linux_O_APPEND);
        /* write access, create file and truncate file to length 0 */
        flagsCreateTruncWrite := IOR(Linux_O_WRONLY, Linux_O_CREAT, Linux_O_TRUNC);
        /* read and write access for the user, read access for the group: rw-r----- */
        mode := 2#110100000; 
    END_IF;
    
    fd := System_open(pathname := path, flags := flagsWriteAppend, ENO => didOpen);
    
    /* file does not exist yet */
    IF NOT(didOpen) THEN
        fd := System_open(pathname := path, flags := flagsCreateTruncWrite, mode := mode, ENO => didOpen);
        Assert(fd >= 0);
    END_IF;
    IF didOpen THEN
        /* modify values of data array */
        data[0] := 16#48;
        data[1] := 16#69;
        System_write(fd := fd, count := 2, data := data, ENO => writeOk);
        Assert(writeOk);
        
        System_close(fd := fd);
        System_delete(pathname := path);
    END_IF;
END_FUNCTION_BLOCK