PL/I preprocessor: Difference between revisions

Revision as of 01:47, 1 August 2014

Revision as of 04:48, 27 November 2016

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*{{code|%IF}} controls the flow of the preprocessor scan according to the value of a preprocessor expression.

<pre>

<source lang="pli">

%IF preprocessor-expression

%THEN preprocessor unit1

%ELSE preprocessor-unit2

</sourcepre>

The preprocessor-units can be any single preprocessor statement or a preprocessor {{code|DO}}-group.

*{{code|%ITERATE}} transfers control to the {{code|%END}} of the containing preprocessor {{code|DO}}-group, ending the current iteration and beginning the next if needed.

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==Example==

The following example for IBM PL/I for OS/2 illustrates the use of a preprocessor procedure to implement a C-like write statement for PL/I.<ref>{{cite web|last=Sturm|first=Eberhard|title=UIO-Makros für Builtin-Funktionen fileread und filewrite|url=http://www.uni-muenster.de/ZIV.EberhardSturm/uio.cpy|accessdate=January 22, 2012}}</ref> The procedure would be called by coding the statement {{code|uwrite file(filename) from(varying_string) count(byte_count);}} <var>Byte_count</var> is optional and defaults to the length of <var>varying_string</var> if omitted.

<pre>

<source lang=PLI>

%uwrite:

procedure keys (File, From, Count);

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%end;

%act uwrite;

</sourcepre>

The statement {{code|uwrite file(file_name) from(var_str) count(64);}} generates the following:

<pre>

<source lang=PLI>

do;

dcl Count00001 fixed bin (15);

Count00001 = filewrite(file_name, ptradd(addr(var_str), 2), min(length(var_str), 64));

end;

</sourcepre>

==Evolution==