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| Writing bytes to IFS stream files using write() ifs C api in RPGLE |
There are following steps involved in writing the bytes to a stream file using write() ifs C api. Let's have a look.
- Create and Open the IFS stream file by calling open() ifs C api in RPGLE.
- Check if file descriptor returned is less than 0, then return from the program.
- Otherwise, if file descriptor is greater or equals 0, then pass file descriptor to write() ifs C api with memory area and length to write stream of bytes to the stream file.
- Check if number of bytes return from the write() ifs C api is less than expected to write, then its an error and display error message to user.
Please refer to Creating and opening IFS stream files using C API open in RPGLE. for better understanding 1st and 2nd point above.
The write() API
The write() API is used to write bytes to a stream file.
The write api needs to know the area of the memory and length. It copies the bytes from memory to disk. Write() api does not care what data resides in the area of memory. It writes everything present in the memory area.
Prototype of write() in C
int write(int fildes, const void *buf, size_t nbyte);
- int: It tells what type of value this write() api returns. The int data type in C is a 32 bits signed integer and is equivalent to "10 I 0" in RPGLE. The write() api returns the number of bytes written to disk. If any error occurs, this number will be less than the number of bytes being asked to write. Therefore, this return value would be used to check for any errors occurred during write to disk.
- write:The write() function attempts to write nbyte bytes to the file associated with the open file descriptor
- int fildes:The first parameter is an integer named File descriptor which is the return value from the open() api and identifies the file being opened.
- const void *buf: The "const" is similar to the RPG "const" keyword which means the write() api will not change the content of this parameter. "void *" means pointer can point to anything like character, number, or a data structure of any number of bytes in memory.
- size_t nbyte: This is the number of bytes to write. Here, "size_t" is user-defined type. Its defined same variable for which we have used LIKE keyword in RPGLE to define it. The byte size is stored idifferently in different platforms. The size_t is defined inside header file "sys/types.h". In IBM i, size_t is defined as 32 bit unsigned integer i.e. RPG "10U 0".
Prototype for write() API in RPGLE
D write PR 10i 0 extproc('write') * 32 bit, no. of byt
D fileds 10i 0 value *file descriptor
D buffer * value * pointer to byte
D noofbytes 10U 0 value * 32 bits
Using write() ifs C api in RPGLE program
RPG Code in Fixed format for Using write() api in RPGLE to Writing bytes to IFS stream files.
HDFTACTGRP(*NO)
D write PR 10i 0 extproc('write') * 32 bit, no. of byt
D fileds 10i 0 value *file descriptor
D buffer * value * pointer to byte
D noofbytes 10U 0 value * 32 bits
D open PR 10I 0 extproc('open')
D ifspath * value options(*string) *ifs path
D oflag 10I 0 value *string of 32 bits
D mode 10U 0 value options(*nopass) * 9 bits
D codepage 10U 0 value options(*nopass) *
* <-----oflag---->
D O_readonly C 1
D O_writeonly C 2
D O_readwrite C 4
D O_createfileifnotexist...
D C 8
D O_exclusivecreate...
D C 16
D O_truncateto0bytes...
D C 64
D O_appendtofile C 256
D O_converttextbycodepage...
D C 8388608
D O_openintextmode...
D C 16777216
*
* <-----mode---->
* owner,group,other (RWX)
* owner authority
D M_readowner C 256
D M_writeowner C 128
D M_executeowner C 64
* group authority
D M_readgroup C 32
D M_writegroup C 16
D M_executegroup C 8
* other people
D M_readother C 4
D M_writeother C 2
D M_executeother C 1
*
Difspath s 512a
Doflag s 10I 0
Dmode s 10U 0
Dcodepage s 10U 0
Dfiledescriptor s 10i 0
*
Difsdata s 500a inz
Dreturn_write s 10i 0 inz
C EVAL ifspath = '/home/easyclass/openfile1'
C EVAL oflag = O_readwrite +
C O_createfileifnotexist
C EVAL mode = M_executeowner
C EVAL filedescriptor = open(%trim(ifspath):
C oflag:
C mode)
C IF filedescriptor < 0
C RETURN
C ENDIF
C EVAL ifsdata = 'TEST IFS WRITE() API'
C EVAL return_write = write(filedescriptor:
C %addr(ifsdata):%size(ifsdata))
C IF return_write < %size(ifsdata)
C 'ERROR' DSPLY
C ENDIF
C EVAL *INLR = *ON
C RETURN
RPG Code in /Free and /End-Free format for Using write() api in RPGLE to Writing bytes to IFS stream files.
HDFTACTGRP(*NO)
D write PR 10i 0 extproc('write') * 32 bit, no. of byt
D fileds 10i 0 value *file descriptor
D buffer * value * pointer to byte
D noofbytes 10U 0 value * 32 bits
D open PR 10I 0 extproc('open')
D ifspath * value options(*string) *ifs path
D oflag 10I 0 value *string of 32 bits
D mode 10U 0 value options(*nopass) * 9 bits
D codepage 10U 0 value options(*nopass) *
* <-----oflag---->
D O_readonly C 1
D O_writeonly C 2
D O_readwrite C 4
D O_createfileifnotexist...
D C 8
D O_exclusivecreate...
D C 16
D O_truncateto0bytes...
D C 64
D O_appendtofile C 256
D O_converttextbycodepage...
D C 8388608
D O_openintextmode...
D C 16777216
*
* <-----mode---->
* owner,group,other (RWX)
* owner authority
D M_readowner C 256
D M_writeowner C 128
D M_executeowner C 64
* group authority
D M_readgroup C 32
D M_writegroup C 16
D M_executegroup C 8
* other people
D M_readother C 4
D M_writeother C 2
D M_executeother C 1
*
Difspath s 512a
Doflag s 10I 0
Dmode s 10U 0
Dcodepage s 10U 0
Dfiledescriptor s 10i 0
*
Difsdata s 500a inz
Dreturn_write s 10i 0 inz
/free
ifspath = '/home/easyclass/openfile1';
oflag = O_readwrite +
O_createfileifnotexist;
mode = M_executeowner;
filedescriptor = open(%trim(ifspath):
oflag:
mode);
if filedescriptor < 0;
return;
endif;
ifsdata = 'TEST IFS WRITE() API';
return_write = write(filedescriptor:%addr(ifsdata):%size(ifsdata));
if return_write < %size(ifsdata);
DSPLY 'ERROR';
endif;
*inlr = *on;
return;
/end-free
RPG Code in Fully Free format for Using write() api in RPGLE to Writing bytes to IFS stream files.
**FREE
CTL-OPT DFTACTGRP(*NO);
DCL-PR write int(10) EXTPROC('write');
fileds int(10) VALUE;
buffer pointer VALUE;
noofbytes uns(10) VALUE;
END-PR;
DCL-PR open int(10) EXTPROC('open');
ifspath pointer VALUE options(*string);
oflag int(10) VALUE;
mode uns(10) VALUE options(*nopass);
codepage uns(10) VALUE options(*nopass);
END-PR;
// * <-----oflag---->
DCL-C O_readonly 1;
DCL-C O_writeonly 2;
DCL-C O_readwrite 4;
DCL-C O_createfileifnotexist 8;
DCL-C O_exclusivecreate 16;
DCL-C O_truncateto0bytes 64;
DCL-C O_appendtofile 256;
DCL-C O_converttextbycodepage 8388608;
DCL-C O_openintextmode 16777216;
// * <-----mode---->
// * owner,group,other (RWX)
// * owner authority
DCL-C M_readowner 256;
DCL-C M_writeowner 128;
DCL-C M_executeowner 64;
// * group authority
DCL-C M_readgroup 32;
DCL-C M_writegroup 16;
DCL-C M_executegroup 8;
// * other people
DCL-C M_readother 4;
DCL-C M_writeother 2;
DCL-C M_executeother 1;
DCL-S ifspath CHAR(512);
DCL-S oflag int(10);
DCL-S mode uns(10);
DCL-S codepage uns(10);
DCL-S filedescriptor int(10);
DCL-S ifsdata char(500) inz;
DCL-S return_write int(10) inz;
ifspath = '/home/easyclass/openfile1';
oflag = O_readwrite +
O_createfileifnotexist;
mode = M_executeowner;
filedescriptor = open(%trim(ifspath):
oflag:
mode);
if filedescriptor < 0;
return;
endif;
ifsdata = 'TEST IFS WRITE() API';
return_write = write(filedescriptor:%addr(ifsdata):%size(ifsdata));
if return_write < %size(ifsdata);
DSPLY 'ERROR';
endif;
*inlr = *on;
return;
Brief Explanation of the RPGLE code using WRITE() ifs C api
Compile-Run-Output of the above program
Browse : /home/EASYCLASS/openfile1
Record : 1 of 4 by 18 Column : 1 132 by 131
Control :
....+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8....+..
************Beginning of data**************
TEST IFS WRITE() API
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