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Tips and Techniques: Compare and Ignore Case

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For years, I hoped IBM would provide RPG IV programmers with the ability to compare two fields while ignoring upper/lowercase. Eventually, I decided to add such a function to my RPG xTools in the form of a CompNoCase() subprocedure.

To use CompNoCase(), you simply add it to an IF statement, as follows:

 

     C                   if        CompNoCase(CMPNAM : 'xyz')
     **  Do something when they are equal
     C                   endif

 

This works very well and is very efficient. But I recently realized that a slightly different variation on the CompNoCase() subprocedure is available in the C runtime library. That function is memicmp(), and you can use it in your RPG IV programs by adding the following prototype to your source code:

 

     D memicmp         PR            10I 0 ExtProc('__memicmp')
     D  pValue1                        *   Value
     D  pValue2                        *   Value
     D  nBufLen                      10U 0 Value

 

In addition, you must include the BNDDIR('QC2LE') keyword on your header specification (H-spec).

This function compares one value to another for the given length. Unlike a "normal" RPG-style compare that ignores trailing blanks, memicmp() uses trailing blanks in the comparison. However, you tell it the number of characters to compare, so this subtle difference really isn't an issue.

The memicmp() procedure begins comparing the two values character by character until either the nCompLen (compare length) value is reached or the two characters at the given position do not match. When the procedure detects a mismatch, the position of the mismatch is returned.

So if the two values are ABCxEFG and abc8efg, memicmp() will return a value of 3 to indicate that in offset 3 the two values don't match. Why 3 and not 4? Because C uses zero-based offsets, rather than absolute positions. You always need to add 1 to the result to determine the correct position.

When I use memicmp(), I tend not to use the result value for anything other than a yes/no test condition, as follows:

C                   if        memicmp(CMPNAM:'xyz':%len(%TrimR(CMPNAM)))=0
**  Do something when they are equal
C                   endif

 

This is the statement:

if  memicmp(CMPNAM:'xyz':%len(%TrimR(CMPNAM)))=0

 

I use %TRIMR to remove trailing blanks. Of course 'xyz' would more than likely be a field or named constant. Use this statement to compare the result of memicmp() to zero. If it equals zero, then the two strings are equal (ignoring upper/lowercase).

Not a bad little function, considering everyone has it on their system today, even if you're still on V4R1.

One caveat about memicmp(): The actual C runtime function name is '__memicmp'. That's two underscore characters followed by a lowercase 'memicmp'. If you put one underscore in your prototype, it will not compile!

The best way to obtain C runtime function prototypes is to download them for free from my Web site. Visit www.rpgiv.com/downloads and then click on the corresponding source file name to view a list of members for downloading. Note: I keep prototypes for C and MI function in a source file named QCPYSRC ("Q Copy Source").

 

 

 

Bob Cozzi is a programmer/consultant, writer/author, and software developer of the RPG xTools, a popular add-on subprocedure library for RPG IV. His book The Modern RPG Language has been the most widely used RPG programming book for nearly two decades. He, along with others, speaks at and runs the highly-popular RPG World conference for RPG programmers.

 

BOB COZZI

Bob Cozzi is a programmer/consultant, writer/author, and software developer. His popular RPG xTools add-on subprocedure library for RPG IV is fast becoming a standard with RPG developers. His book The Modern RPG Language has been the most widely used RPG programming book for more than a decade. He, along with others, speaks at and produces the highly popular RPG World conference for RPG programmers.

MC Press books written by Robert Cozzi available now on the MC Press Bookstore.

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