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<h1 class="topictitle1">Examples: UNIX-type APIs</h1>
<div><p>This simple example program illustrates the use of several integrated
file system functions. </p>
<div class="section"><div class="note"><span class="notetitle">Note:</span> Read the <a href="codedisclaimer.htm">Code license and disclaimer information</a> for important
legal information.</div>
<p>The program performs the following
operations:</p>
<dl><dt class="dlterm">(1)</dt>
<dd>Uses the <span class="uicontrol">getuid()</span> function to determine the real
user ID (uid).</dd>
<dt class="dlterm">(2)</dt>
<dd>Uses the <span class="uicontrol">getcwd()</span> function to determine the current
directory.</dd>
<dt class="dlterm">(3)</dt>
<dd>Uses the <span class="uicontrol">open()</span> function to create a file. The
owner (the person who created the file) is given read, write, and execute
authority to the file.</dd>
<dt class="dlterm">(4)</dt>
<dd>Uses the <span class="uicontrol">write()</span> function to write a byte string
to the file. The file is identified by the file descriptor that was provided
in the open operation (<span class="uicontrol">(3)</span>).</dd>
<dt class="dlterm">(5)</dt>
<dd>Uses the <span class="uicontrol">close()</span> function to close the file.</dd>
<dt class="dlterm">(6)</dt>
<dd>Uses the <span class="uicontrol">open()</span> function to open the file for read
only.</dd>
<dt class="dlterm">(7)</dt>
<dd>Uses the <span class="uicontrol">read()</span> function to read a byte string
from the file. The file is identified by the file descriptor that was provided
in the open operation (<span class="uicontrol">(6)</span>).</dd>
<dt class="dlterm">(8)</dt>
<dd>Uses the <span class="uicontrol">close()</span> function to close the file.</dd>
<dt class="dlterm">(9)</dt>
<dd>Uses the <span class="uicontrol">unlink()</span> function to remove the link to
the file.</dd>
</dl>
</div>
<div class="section"><h4 class="sectiontitle">Example in ILE C: Using the Integrated File System</h4><p>This
example program uses the integrated file system from ILE C.</p>
<pre>/********************************************************************/
/* */
/* Language: ILE C */
/* */
/* Description: Demonstrate use of integrated file system */
/* from ILE C */
/* */
/********************************************************************/
#include &lt;stdlib.h&gt;
#include &lt;stdio.h&gt;
#include &lt;fcntl.h&gt;
#include &lt;unistd.h&gt;
#include &lt;sys/types.h&gt;
#define BUFFER_SIZE 2048
#define TEST_FILE "test.file"
#define TEST_DATA "Hello World!"
#define USER_ID "user_id_"
char InitialFile[BUFFER_SIZE];
char InitialDirectory[BUFFER_SIZE] = ".";
char Buffer[32];
int FilDes = -1;
int BytesRead;
int BytesWritten;
uid_t UserID;
void CleanUpOnError(int level)
{
printf("Error encountered, cleaning up.\n");
switch ( level )
{
case 1:
printf("Could not get current working directory.\n");
break;
case 2:
printf("Could not create file %s.\n",TEST_FILE);
break;
case 3:
printf("Could not write to file %s.\n",TEST_FILE);
close(FilDes);
unlink(TEST_FILE);
break;
case 4:
printf("Could not close file %s.\n",TEST_FILE);
close(FilDes);
unlink(TEST_FILE);
break;
case 5:
printf("Could not open file %s.\n",TEST_FILE);
unlink(TEST_FILE);
break;
case 6:
printf("Could not read file %s.\n",TEST_FILE);
close(FilDes);
unlink(TEST_FILE);
break;
case 7:
printf("Could not close file %s.\n",TEST_FILE);
close(FilDes);
unlink(TEST_FILE);
break;
case 8:
printf("Could not unlink file %s.\n",TEST_FILE);
unlink(TEST_FILE);
break;
default:
break;
}
printf("Program ended with Error.\n"\
"All test files and directories may not have been removed.\n");
}
int main ()
{
<span class="uicontrol">(1)</span>
/* Get and print the real user id with the getuid() function. */
UserID = getuid();
printf("The real user id is %u. \n",UserID);
<span class="uicontrol">(2)</span>
/* Get the current working directory and store it in InitialDirectory. */
if ( NULL == getcwd(InitialDirectory,BUFFER_SIZE) )
{
perror("getcwd Error");
CleanUpOnError(1);
return 0;
}
printf("The current working directory is %s. \n",InitialDirectory);
<span class="uicontrol">(3)</span>
/* Create the file TEST_FILE for writing, if it does not exist.
Give the owner authority to read, write, and execute. */
FilDes = open(TEST_FILE, O_WRONLY | O_CREAT | O_EXCL, S_IRWXU);
if ( -1 == FilDes )
{
perror("open Error");
CleanUpOnError(2);
return 0;
}
printf("Created %s in directory %s.\n",TEST_FILE,InitialDirectory);
<span class="uicontrol">(4)</span>
/* Write TEST_DATA to TEST_FILE via FilDes */
BytesWritten = write(FilDes,TEST_DATA,strlen(TEST_DATA));
if ( -1 == BytesWritten )
{
perror("write Error");
CleanUpOnError(3);
return 0;
}
printf("Wrote %s to file %s.\n",TEST_DATA,TEST_FILE);
<span class="uicontrol">(5)</span>
/* Close TEST_FILE via FilDes */
if ( -1 == close(FilDes) )
{
perror("close Error");
CleanUpOnError(4);
return 0;
}
FilDes = -1;
printf("File %s closed.\n",TEST_FILE);
<span class="uicontrol">(6)</span>
/* Open the TEST_FILE file for reading only. */
if ( -1 == (FilDes = open(TEST_FILE,O_RDONLY)) )
{
perror("open Error");
CleanUpOnError(5);
return 0;
}
printf("Opened %s for reading.\n",TEST_FILE);
<span class="uicontrol">(7)</span>
/* Read from the TEST_FILE file, via FilDes, into Buffer. */
BytesRead = read(FilDes,Buffer,sizeof(Buffer));
if ( -1 == BytesRead )
{
perror("read Error");
CleanUpOnError(6);
return 0;
}
printf("Read %s from %s.\n",Buffer,TEST_FILE);
if ( BytesRead != BytesWritten )
{
printf("WARNING: the number of bytes read is "\
"not equal to the number of bytes written.\n");
}
<span class="uicontrol">(8)</span>
/* Close the TEST_FILE file via FilDes. */
if ( -1 == close(FilDes) )
{
perror("close Error");
CleanUpOnError(7);
return 0;
}
FilDes = -1;
printf("Closed %s.\n",TEST_FILE);
<span class="uicontrol">(9)</span>
/* Unlink the file TEST_FILE */
if ( -1 == unlink(TEST_FILE) )
{
perror("unlink Error");
CleanUpOnError(8);
return 0;
}
printf("Unlinking file %s.\n",TEST_FILE);
printf("Program completed successfully.\n");
return 0;
}</pre>
</div>
<div class="section"><h4 class="sectiontitle">Example in ILE COBOL: Using the Integrated File System</h4><p>This
example program uses the integrated file system from ILE COBOL.</p>
<pre> PROCESS NOMONOPRC.
IDENTIFICATION DIVISION.
***************************************************************
***************************************************************
*
* Language: COBOL
*
* Description: Demonstrate use of integrated file system
* from ILE COBOL
*
***************************************************************
*
***************************************************************
PROGRAM-ID. IFS.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. IBM-AS400.
OBJECT-COMPUTER. IBM-AS400.
SPECIAL-NAMES.
* LINKAGE TYPE PROCEDURE FOR "geterrno",
LINKAGE TYPE PROCEDURE FOR "getuid",
LINKAGE TYPE PROCEDURE FOR "getcwd",
LINKAGE TYPE PROCEDURE FOR "open",
LINKAGE TYPE PROCEDURE FOR "write",
LINKAGE TYPE PROCEDURE FOR "close",
LINKAGE TYPE PROCEDURE FOR "read",
LINKAGE TYPE PROCEDURE FOR "unlink".
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT LISTING ASSIGN TO PRINTER-QPRINT
ORGANIZATION IS SEQUENTIAL.
DATA DIVISION.
*
FILE SECTION.
FD LISTING RECORD CONTAINS 132 CHARACTERS
LABEL RECORDS ARE STANDARD
DATA RECORD IS LIST-LINE.
01 LIST-LINE PIC X(132).
*
WORKING-STORAGE SECTION.
*
* Report lines
*
01 REALID.
05 PRT-TEXT PIC X(20) VALUE "The real user id is ".
05 USER PIC X(12).
01 CURDIR.
05 PRT-TEXT PIC X(21) VALUE "Current directory is ".
05 INITIALDIR PIC X(100).
01 NEWFIL.
05 PRT-TEXT PIC X(20) VALUE "Created file: ".
05 FILENAME PIC X(100).
01 DATAIN.
05 PRT-TEXT PIC X(20) VALUE "Successfully read: ".
05 DATA-READ PIC X(100).
01 ERRLIN.
05 PRT-TEXT PIC X(20) VALUE "The errno value is: ".
05 ERRVAL PIC X(12).
*
* Miscellaneous elements
*
01 BUFFER PIC X(32767).
01 LENGTH-OF-BUFFER PIC S9(09) BINARY VALUE 32767.
01 TESTFILE.
05 TEST-FILE PIC X(09) VALUE "test.file".
05 NULL-TERMINATE PIC X(01) VALUE LOW-VALUE.
01 OFLAG PIC X(04) VALUE X"0000001A".
01 OFLAG-READ PIC X(04) VALUE X"00000001".
01 OMODE PIC X(04) VALUE X"000001C0".
01 TEST-DATA PIC X(12) VALUE "Hello World!".
01 SIZE-TEST-DATA PIC S9(09) BINARY VALUE 12.
01 FILE-DESCRIPTOR PIC S9(09) BINARY.
01 BYTES-READ PIC S9(09) BINARY.
01 BYTES-WRITTEN PIC S9(09) BINARY.
01 RETURN-INT PIC S9(09) BINARY.
01 RETURN-PTR POINTER.
*
* Beginning of mainline
*
PROCEDURE DIVISION.
MAIN-LINE.
OPEN OUTPUT LISTING.
*
* Get and print the real user id with the getuid function.
*
CALL "getuid" GIVING RETURN-INT.
*
* Check for error and report status.
*
IF RETURN-INT = -1 MOVE "Error getting real user id"
TO LIST-LINE,
PERFORM ERROR-FOUND,
ELSE MOVE RETURN-INT TO USER,
WRITE LIST-LINE FROM REALID.
*
* Get the current working directory and store it in BUFFER
*
CALL "getcwd" USING BY VALUE ADDRESS OF BUFFER,
BY VALUE LENGTH-OF-BUFFER,
GIVING RETURN-PTR.
*
* Check for error and report status.
*
IF RETURN-PTR = NULL MOVE "Error getting real current dir"
TO LIST-LINE,
PERFORM ERROR-FOUND,
ELSE MOVE BUFFER TO INITIALDIR,
WRITE LIST-LINE FROM CURDIR.
*
* Create the file test.file for writing. If it does not exist,
* give the owner authority to read, write, and execute.
*
CALL "open" USING BY VALUE ADDRESS OF TESTFILE,
BY VALUE OFLAG,
BY VALUE OMODE,
GIVING FILE-DESCRIPTOR.
*
* Check for error and report status.
*
IF FILE-DESCRIPTOR = -1 MOVE "Could not create file"
TO LIST-LINE,
PERFORM ERROR-FOUND,
ELSE MOVE TEST-FILE TO FILENAME,
WRITE LIST-LINE FROM NEWFIL.
*
* Write TEST-DATA to test.file via file descriptor from open
*
CALL "write" USING BY VALUE FILE-DESCRIPTOR,
BY VALUE ADDRESS OF TEST-DATA,
BY VALUE SIZE-TEST-DATA,
GIVING BYTES-WRITTEN.
*
* Check for error and report status.
*
IF BYTES-WRITTEN = -1 MOVE "Could not write to file"
TO LIST-LINE,
PERFORM ERROR-FOUND,
ELSE MOVE "Wrote to file successfully"
TO LIST-LINE,
WRITE LIST-LINE.
*
* Close test.file via file descriptor
*
CALL "close" USING BY VALUE FILE-DESCRIPTOR,
GIVING RETURN-INT.
*
* Check for error and report status.
*
IF RETURN-INT = -1 MOVE "Could not close file"
TO LIST-LINE,
PERFORM ERROR-FOUND,
ELSE MOVE "Successfully closed file"
TO LIST-LINE,
WRITE LIST-LINE.
*
* Open the file test.file for reading.
*
CALL "open" USING BY VALUE ADDRESS OF TESTFILE,
BY VALUE OFLAG-READ,
GIVING FILE-DESCRIPTOR.
*
* Check for error and report status.
*
IF FILE-DESCRIPTOR = -1 MOVE "Could not open file"
TO LIST-LINE,
PERFORM ERROR-FOUND,
ELSE MOVE "File open successful"
TO LIST-LINE,
WRITE LIST-LINE.
*
* Read from test.file via file descriptor from open
*
CALL "read" USING BY VALUE FILE-DESCRIPTOR,
BY VALUE ADDRESS OF BUFFER,
BY VALUE LENGTH-OF-BUFFER,
GIVING BYTES-READ.
*
* Check for error and report status.
*
IF BYTES-READ = -1 MOVE "Read failed"
TO LIST-LINE,
PERFORM ERROR-FOUND,
ELSE IF BYTES-READ = BYTES-WRITTEN
MOVE BUFFER TO DATA-READ,
WRITE LIST-LINE FROM DATAIN,
ELSE MOVE "Data Truncation on Read"
TO LIST-LINE,
PERFORM ERROR-FOUND.
*
* Close test.file via file descriptor
*
CALL "close" USING BY VALUE FILE-DESCRIPTOR,
GIVING RETURN-INT.
*
* Check for error and report status.
*
IF RETURN-INT = -1 MOVE "Could not close file"
TO LIST-LINE,
PERFORM ERROR-FOUND,
ELSE MOVE "Successfully closed file"
TO LIST-LINE,
WRITE LIST-LINE.
*
* Unlink test.file
*
CALL "unlink" USING BY VALUE ADDRESS OF TESTFILE,
GIVING RETURN-INT.
*
* Check for error and report status.
*
IF RETURN-INT = -1 MOVE "Unlink of file failed"
TO LIST-LINE,
PERFORM ERROR-FOUND,
ELSE MOVE "Unlink of file successful"
TO LIST-LINE,
WRITE LIST-LINE.
*
MOVE "Program run is successful" TO LIST-LINE.
WRITE LIST-LINE.
STOP RUN.
*
* End of MAINLINE
*
*
* Common error reporting subroutine
*
* If errors occur, the Integrated File System exports the
* variable 'errno' to assist in determining the problem. As
* 'errno' is lowercase, ILE COBOL cannot directly import this
* variable and must use a C module to access it. If the
* developer has ILE C available, the following sample C code
* will import 'errno' and make it available to the COBOL
* application
*
* #include &lt;errno.h&gt;
* int geterrno()
* {
* return errno;
* }
*
* To activate this C module remove the comment identifiers
* following the WRITE statement and remove the comment
* identifier from the geterrno declaration in the Configuration
* Section. Definitions for the returned errno are found in
* file QSYSINC/SYS member ERRNO.
*
ERROR-FOUND.
WRITE LIST-LINE.
* CALL "geterrno" GIVING RETURN-INT.
* MOVE RETURN-INT TO ERRVAL.
* WRITE LIST-LINE FROM ERRLIN.
STOP RUN.</pre>
</div>
<div class="section"><h4 class="sectiontitle">Example in ILE RPG: Using the Integrated File System</h4><p>This
example program uses the integrated file system from ILE RPG.</p>
<pre> F********************************************************************
F*
F* Language: ILE RPG
F*
F* Description: Demonstrate use of integrated file system
F* from ILE RPG
F*
F********************************************************************
FQSYSPRT O F 132 PRINTER
D*
D* Prototype the Integrated File System APIs
D*
Dgetuid PR 9B 0 EXTPROC('getuid')
Dgetcwd PR * EXTPROC('getcwd')
D * VALUE
D 9B 0 VALUE
Dopen PR 9B 0 EXTPROC('open')
D * VALUE
D 4A VALUE
D 4A VALUE
Dwrite PR 9B 0 EXTPROC('write')
D 9B 0 VALUE
D * VALUE
D 9B 0 VALUE
Dclose PR 9B 0 EXTPROC('close')
D 9B 0 VALUE
Dopen2 PR 9B 0 EXTPROC('open')
D * VALUE
D 4A VALUE
Dread PR 9B 0 EXTPROC('read')
D 9B 0 VALUE
D * VALUE
D 9B 0 VALUE
Dunlink PR 9B 0 EXTPROC('unlink')
D * VALUE
D*
D* errno prototype; see error subroutine for further information
D*
D*errno PR 9B 0 EXTPROC('geterrno')
DUser S 12A
DBuffer S 32767A
DReturnPtr S *
DReturnInt S 9B 0
DFileDesc S 9B 0
Dtest_file S 2048A INZ('test.file')
DInitialDir S 2048A
Dtest_data S 12A INZ('Hello World!')
DBytesWrt S 9B 0
DBytesRead S 9B 0
DFileName S 2049A
DPrintLine S 100A
DNull C CONST(X'00')
C*
C* Get and print the real user id with the getuid function.
C*
C eval ReturnInt = getuid
C*
C* Check for error and report status.
C*
C if ReturnInt = -1
C eval PrintLine = 'Error getting real user id'
C exsr error
C eval *INLR = '1'
C return
C else
C move ReturnInt User
C eval PrintLine = 'The real user id is '
C + %TRIML(User)
C except
C endif
C*
C* Get the current working directory and store it in Buffer.
C*
C eval ReturnPtr=getcwd(%ADDR(Buffer)
C : %SIZE(Buffer))
C*
C* Check for error and report status.
C*
C if ReturnPtr = *NULL
C eval PrintLine = 'Error getting current directory'
C exsr error
C eval *INLR = '1'
C return
C else
C*
C* Print current directory name remembering to scan for null terminator.
C*
C Null scan Buffer NullFound 5 0
C eval InitialDir = %SUBST(Buffer&amp;#58;1&amp;#58;NullFound)
C eval PrintLine = 'Current Directory is '
C + InitialDir
C except
C endif
C*
C* Create the file TEST_FILE for writing. If it does not exist,
C* give the owner authority to read, write, and execute.
C*
C eval FileName = %TRIMR(test_file) + Null
C eval FileDesc = open(%ADDR(FileName)
C : x'0000001A' : x'000001C0')
C*
C* Check for error and report status.
C*
C if FileDesc = -1
C eval PrintLine = 'Could not create file'
C exsr error
C eval *INLR = '1'
C return
C else
C eval PrintLine = 'File '
C + %TRIMR(test_file)
C + ' created successfully'
C except
C end
C*
C* Write test_data to test_file via FileDesc returned by open
C*
C eval BytesWrt = write(FileDesc
C : %ADDR(Test_Data)
C : %SIZE(Test_Data))
C*
C* Check for error and report status. If an error occurs,
C* attempt cleanup.
C*
C if BytesWrt = -1
C eval PrintLine = 'Could not write to file'
C exsr error
C eval ReturnInt = close(FileDesc)
C eval ReturnInt = unlink(%ADDR(FileName))
C eval *INLR = '1'
C return
C else
C eval PrintLine = 'Wrote to '
C + %TRIMR(test_file)
C + ' successfully'
C except
C endif
C*
C* Close test_file via FileDesc
C*
C eval ReturnInt = close(FileDesc)
C*
C* Check for error and report status. If an error occurs,
C* attempt cleanup.
C*
C if ReturnInt = -1
C eval PrintLine = 'Could not close file'
C exsr error
C eval ReturnInt = close(FileDesc)
C eval ReturnInt = unlink(%ADDR(FileName))
C eval *INLR = '1'
C return
C else
C eval PrintLine = 'File '
C + %TRIMR(test_file)
C + ' closed successfully'
C except
C endif
C*
C* Open the file for read only
C*
C eval FileDesc = open2(%ADDR(FileName)
C : x'00000001')
C*
C* Check for error and report status. If an error occurs,
C* attempt cleanup.
C*
C if FileDesc = -1
C eval PrintLine = 'Open of file failed'
C exsr error
C eval ReturnInt = unlink(%ADDR(FileName))
C eval *INLR = '1'
C return
C else
C eval PrintLine = 'Open of file successful'
C except
C endif
C*
C* Read from file
C*
C eval BytesRead = read(FileDesc
C : %ADDR(Buffer) : %SIZE(Buffer))
C*
C* Check for error and report status. If an error occurs,
C* attempt cleanup.
C*
C if BytesRead = -1
C eval PrintLine = 'Read failed'
C exsr error
C eval ReturnInt = close(FileDesc)
C eval ReturnInt = unlink(%ADDR(FileName))
C eval *INLR = '1'
C return
C else
C if BytesRead = BytesWrt
C eval PrintLine = 'Data successfully read: '
C + %TRIMR(Buffer)
C else
C eval PrintLine = 'Data truncation on read'
C endif
C except
C endif
C*
C* Close the LinkName file
C*
C eval ReturnInt = close(FileDesc)
C*
C* Check for error and report status. If an error occurs,
C* attempt cleanup.
C*
C if ReturnInt = -1
C eval PrintLine = 'Close of link failed'
C exsr error
C eval ReturnInt = close(FileDesc)
C eval ReturnInt = unlink(%ADDR(FileName))
C eval *INLR = '1'
C return
C else
C eval PrintLine = 'Close of link successful'
C except
C endif
C*
C* Unlink test_file
C*
C eval ReturnInt = unlink(%ADDR(FileName))
C*
C* Check for error and report status. If an error occurs,
C* attempt cleanup.
C*
C if ReturnInt = -1
C eval PrintLine = 'Unlink of file failed'
C exsr error
C eval ReturnInt = unlink(%ADDR(FileName))
C eval *INLR = '1'
C return
C else
C eval PrintLine = 'Unlink of file successful'
C except
C endif
C*
C* End of main program
C*
C eval PrintLine = 'Program run is successful'
C except
C eval *INLR = '1'
C return
C*
C* Common error reporting subroutine
C*
C* If errors occur, the integrated file system exports the variable
C* 'errno' to assist in determining the problem. As 'errno' is
C* lowercase, ILE RPG cannot directly import this variable and must
C* use a C module to access it. If the developer has ILE C
C* available, the following sample C code will import 'errno' and
C* make it available to the RPG application.
C*
C* #include &lt;errno.h&gt;
C* int geterrno()
C* {
C* return errno;
C* }
C*
C* To activate this C module, remove the four comment identifiers
C* following the 'except' statement and remove the comment identifier
C* from the errno prototype. Definitions for the returned errno
C* are found in the file QSYSINC/SYS member ERRNO.
C*
C error begsr
C except
C* eval ReturnInt = errno
C* move ReturnInt Errnoval 9
C* eval PrintLine = 'Errno is ' + Errnoval
C* except
C eval PrintLine = 'Program ended in error'
C except
C endsr
OQSYSPRT E 1
O PrintLine 100</pre>
</div>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="unixType.htm" title="The interfaces provided by sockets, the integrated file system, and other categories are part of a continuing emphasis on supporting an open environment on the system.">APIs for the UNIX-type environment</a></div>
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