Fortran77: Checking if character array index is empty

Question

I have a character array names(10)*6. I'm looping through I = 1:10 and writing the values of names(I).

The problem is that names periodically is missing values, and if thats the case for a particular names(I), I want to skip it.

I was trying to do something like this.

   IF(names(I) .NE. 0) THEN 
        WRITE(4,202) names(I)   
    ENDIF

I got an error telling me I'm dumb for comparing characters to 0. That makes sense. What should I compare it to? Empty spaces like this? How do I check if its not defined or empty after I declared space for it?

IF(mychar(I) .NE. '      ') THEN 
     WRITE(4,202) names(I)  
ENDIF

The goal is to only issue the write command if there is actually something there. :-)

Edit Note: I may not initialize this array. I am wondering what the default value for an undefined declared index is, or if there is a function to check if a character array index is empty.

Why not initialize it to an empty string prior to usage? Then, you can do the check you proposed... — Alexander Vogt
– Alexander Vogt, Commented Jun 25, 2014 at 14:43
Describe the situation in more detail in the question. Show what you really want to achieve, not just what you mistakenly think is the right way how to do it. — Vladimir F Героям слава
– Vladimir F Героям слава, Commented Jun 25, 2014 at 15:37
fortran strings are blank padded, so LEN_TRIM(string).eq.0 , string.eq.'' , and string.eq.' ' are all equivalent. ( And all will likely be false if the string was never initialised. ) — agentp
– agentp, Commented Jun 25, 2014 at 18:54
Response to the "Edit note". By "undefined" I assume that you mean "uninitialized". Fortran provides no default values for uninitialized variables. You should initialize the variable before comparing it. However, when you assign to a string with a shorter string, the remaining trailing characters are filled with blanks. Perhaps that it what you are asking. — M. S. B.
– M. S. B., Commented Jun 26, 2014 at 2:43

High Performance Mark · Accepted Answer · 2014-06-25 16:23:44Z

1

You might be interested in the intrinsic len_trim function. As always Read The Fortran Manual.

answered Jun 25, 2014 at 16:23

High Performance Mark

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1 Comment

Andrew Over a year ago

I think this will be an effective way to check if it has been defined, I will try it out. Thank you for the response.

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