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<meta name="DC.Title" content="Pass parameters" />
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<meta name="abstract" content="When you pass control to another program or procedure, you can also pass information to it for modification or use within the receiving program or procedure." />
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<title>Pass parameters</title>
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<body id="passp"><a name="passp"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Pass parameters</h1>
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<div><p>When you pass control to another program or procedure, you can
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also pass information to it for modification or use within the receiving program
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or procedure. </p>
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<div class="section"> <p> You can specify the information to be passed on the PARM parameter
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on the <span class="cmdname">Call (CALL)</span> command or the <span class="cmdname">Call Bound Procedure
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(CALLPRC)</span> command. The characteristics and requirements for these
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commands are slightly different.</p>
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<p>For instance, if PROGA contains the
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following command: </p>
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<pre>CALL PROGB PARM(&AREA)</pre>
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<p>then it calls PROGB and passes the value of &AREA to it.
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PROGB must start with the PGM command, which also must specify the parameter
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it is to receive:</p>
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<pre>PGM PARM(&AREA) /* PROGB */</pre>
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<p>For the <span class="cmdname">Call (CALL)</span> command or the <span class="cmdname">Call
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Bound Procedure (CALLPRC)</span> command, you must specify the parameters
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passed on the PARM parameter, and you must specify them on the PARM parameter
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of the PGM command in the receiving program or procedure. Because parameters
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are passed by position, not name, the position of the value passed in the <span class="cmdname">Call
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(CALL)</span> command or the <span class="cmdname">Call Bound Procedure (CALLPRC)</span> command
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must be the same as its position on the receiving PGM command. For example,
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if PROGA contains the following command:</p>
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<pre>CALL PROGB PARM(&A &B &C ABC)</pre>
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<p>it passes three variables and a character string, and if PROGB
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starts with:</p>
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<pre>PGM PARM(&C &B &A &D) /*PROGB*/</pre>
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<p>then the value of &A in PROGA is used for &C in PROGB,
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and so on; &D in PROGB is <samp class="codeph">ABC</samp>. The order of the DCL
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statements in PROGB is unimportant. Only the order in which the parameters
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are specified on the PGM statement determines what variables are passed.</p>
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<p>In
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addition to the position of the parameters, you must pay careful attention
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to their length and type. Parameters listed in the receiving procedure or
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program must be declared as the same length and type as they are in the calling
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procedure or program. Decimal constants are always passed with a length of <samp class="codeph">(15 5)</samp>.</p>
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<p>When
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you use the <span class="cmdname">Call Bound Procedure (CALLPRC)</span> command and
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pass character string constants, you must specify the exact number of bytes,
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and pass exactly that number. The called procedure can use the information
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in the operational descriptor to determine the exact number of bytes passed.
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You can use the API CEEDOD to access the operational descriptor. </p>
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<p>When
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you use the CALL command, character string constants of 32 bytes or less are
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always passed with a length of 32 bytes. If the string is longer than 32,
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you must specify the exact number of bytes, and pass exactly that number.</p>
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<p>The
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following is an example of a procedure or program that receives the value &VAR1:
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</p>
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<pre>PGM PARM(&VAR1) /*PGMA*/
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DCL VAR1 *CHAR LEN(36)
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.
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.
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.
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ENDPGM</pre>
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<p>The CALL command or <span class="cmdname">Call Bound Procedure (CALLPRC)</span> command
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must specify 36 characters: </p>
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<pre>CALLPRC PGMA(ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJ)</pre>
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<p>The following example specifies the default lengths: </p>
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<pre>PGM PARM(&P1 &P2)
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DCL VAR(&P1) TYPE(*CHAR) LEN(32)
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DCL VAR(&P2) TYPE(*DEC) LEN(15 5)
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IF (&P1 *EQ DATA) THEN(CALL MYPROG &P2)
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ENDPGM</pre>
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<p>To call this program, you could specify: </p>
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<pre>CALL PROG (DATA 136)</pre>
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<p>The character string DATA is passed to &P1; the decimal
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value 136 is passed to &P2</p>
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<p>Referring to locally defined variables
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incurs less overhead than referring to passed variables. Therefore, if the
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called procedure or program frequently refers to passed variables, performance
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can be improved by copying the passed values into a local variable and referring
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to the locally defined value rather than the passed value.</p>
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<p>When calling
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an OPM CL program, the number of parameters that are passed to it must exactly
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match the number that is expected by the program. The number that is expected
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is determined at the time the program is created. (The operating system prevents
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you from calling a program with more or fewer parameters than the program
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expects). When calling an ILE program or procedure, the operating system does
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not check the number of parameters that are passed on the call. In addition,
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the space where the operating system stores the parameters is not reinitialized
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between procedure calls. Calling a procedure that expects "n" parameters with
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"n-1" parameters makes the system use whatever is in the parameter space to
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access the "nth" parameter. The results of this action are very unpredictable.
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This also applies to procedures written in other ILE languages that call CL
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procedures or are called by CL procedures.</p>
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<p>This also gives you more
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flexibility when you write ILE CL procedures, because you can write procedures
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that have variable length parameter lists. For example, based on the value
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of one parameter, a parameter that is specified later in the list may not
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be required. If the controlling parameter indicated an unspecified optional
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parameter, the called procedure should not attempt to refer to the optional
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parameter.</p>
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<p>You can also specify the special value *OMIT for any parameter
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that you want to omit from the parameter list. If you specify *OMIT for a
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parameter, the calling procedure passes a null pointer. The procedure that
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is called has to be prepared to handle a null pointer if it refers to a parameter
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that is omitted. In control language (CL), you can check for a null pointer
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by monitoring for MCH3601 on the first reference to the omittable parameter.
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The procedure must take appropriate action if it receives a MCH3601.</p>
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<p>When
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calling procedures, you can pass arguments by reference and by value.</p>
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<p>The
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following example has two CL procedures. The first procedure expects one parameter;
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if that parameter remains unspecified, results will be unpredictable. The
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first procedure calls another procedure, PROC1. PROC1 expects one or two parameters.
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If the value of the first parameter is '1', it expects the second parameter
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as specified. If the value of the second parameter is '0', it assumes that
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the second parameter remained unspecified and used a default value instead.
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PROC1 also uses the CEEDOD API to determine the actual length that is passed
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for the second parameter.</p>
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<div class="note"><span class="notetitle">Note:</span> Read the <a href="codedisclaimer.htm">Code license and disclaimer information</a> for
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important legal information.</div>
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<div class="fignone"><pre>MAIN: PGM PARM(&TEXT)/* &TEXT must be specified. Results will be +
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unpredictable if it is omitted.*/
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DCL VAR(&TEXT) TYPE(*CHAR) LEN(10)
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CALLPRC PRC(PROC1) PARM('0')
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CALLPRC PRC(PROC1) PARM('1' &TEXT)
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CALLPRC PRC(PROC1) PARM('1' 'Goodbye')
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ENDPGM
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PROC1: PGM PARM(&P1 &P2) /* PROC1 - Procedure with optional +
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parameter &P2 */
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DCL VAR(&P1) TYPE(*LGL) /*Flag which indicates +
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whether or not &P2 will be specified. If +
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value is '1', then &P2 is specified */
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DCL VAR(&P2) TYPE(*CHAR) LEN(10)
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DCL VAR(&MSG) TYPE(*CHAR) LEN(10)
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DCL VAR(&PARMPOS) TYPE(*CHAR) LEN(4) /* +
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Parameter position for CEEDOD*/
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DCL VAR(&PARMDESC) TYPE(*CHAR) LEN(4) /* +
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Parameter description for CEEDOD*/
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DCL VAR(&PARMTYPE) TYPE(*CHAR) LEN(4) /* +
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Parameter datatype from CEEDOD*/
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DCL VAR(&PARMINFO1) TYPE(*CHAR) LEN(4) /* +
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Parameter information from CEEDOD */
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DCL VAR(&PARMINFO2) TYPE(*CHAR) LEN(4) /* +
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Parameter information from CEEDOD */
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DCL VAR(&PARMLEN) TYPE(*CHAR) LEN(4) /* +
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Parameter length from CEEDOD*/
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DCL VAR(&PARMLEND) TYPE(*DEC) LEN(3 0) /* +
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Decimal form of parameter length*/
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IF COND(&P1) THEN(DO) /* Parm 2 is+
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specified, so use the parm value for the +
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message text*/
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CHGVAR VAR(%BIN(&PARMPOS 1 4)) VALUE(2) /* Tell +
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CEEDOD that we want the operational +
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descriptor for the second parameter*/
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CALLPRC PRC(CEEDOD) PARM(&PARMPOS &PARMDESC +
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&PARMTYPE &PARMINFO1 &PARMINFO2 &PARMLEN) +
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/* Call CEEDOD to get the length of data +
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specified for &P2*/
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CHGVAR VAR(&PARMLEND) VALUE(%BIN(&PARMLEN 1 4)) /* +
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Convert the length returned by CEEDOD to +
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decimal format*/
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CHGVAR VAR(&MSG) VALUE(%SST(&P2 1 &PARMLEND)) /* +
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Copy the data passed in to a local variable*/
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ENDO
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ELSE CMD(CHGVAR VAR(%MSG) VALUE('Hello')) /* Use +
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"Hello" for the message text*/
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SNDPGMMSG MSG(&MSG)
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ENDPGM
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</pre>
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</div>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="ucall.htm">CALL command</a></strong><br />
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When the CALL command is issued by a CL procedure, each parameter value passed to the called program can be a character string constant, a numeric constant, a logical constant, or a CL variable.</li>
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<li class="ulchildlink"><strong><a href="comer.htm">Common errors when calling programs and procedures</a></strong><br />
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This describes the errors encountered most frequently in passing values on a CALL command or a CALLPRC command. Some of these errors can be very difficult to debug, and some have serious consequences for program functions.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="cflow.htm" title="You can use the Call Program (CALL), Call Bound Procedure (CALLPRC), and Return (RETURN) commands to pass control back and forth between programs and procedures.">Control flow and communicate between programs and procedures</a></div>
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</div>
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<div class="reltasks"><strong>Related tasks</strong><br />
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<div><a href="callc.htm" title="The Call Program (CALL) command calls a program named on the command, and passes control to it.">Use the CALL command</a></div>
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<div><a href="callp.htm" title="The Call Bound Procedure (CALLPRC) command calls a procedure named on the command, and passes control to it.">Use the CALLPRC command</a></div>
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<div><a href="tfr.htm" title="This is an example of transferring control to improve performance.">Example: Use the Transfer Control (TFRCTL) command</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../cl/callprc.htm">Call Bound Procedure (CALLPRC) command</a></div>
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<div><a href="../cl/call.htm">Call (CALL) command</a></div>
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<div><a href="../apis/CEEDOD.htm">Retrieve Operational Descriptor Information (CEEDOD) API</a></div>
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<div><a href="../books/sc415606.pdf" target="_blank">ILE Concepts PDF</a></div>
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</div>
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</div>
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</body>
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</html>
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