strange behavior with fopen

I have a variable which is a string. When I call fopen with it, it returns -1. When I make the exact same call with fopen by evaluating the string variable, it opens correctly. THis is on a Linux system. Here is a sample of what I'm talking about using the command line:

K>> ischar(testdata.fullfn)
ans = 1

K>> testdata.fullfn
ans = '/home/data/blah.txt'

K>> fid = fopen(testdata.fullfn, 'r')
ans = -1  (open fails)

K>> fid = fopen ('/home/data/blah.txt', 'r')
ans = 3  (open succeeds)

Thus, the file is not open in some other app, the specified path and file exist, I have permission to read it ... but for some reason, fopen does not like the variable! Any ideas? Thanks in advance!

[Steven Lord]

Call fopen with two output arguments and show us what the contents of the second output are when fopen returns -1.

[Guillaume]

and what does

strcmp(testdata.fullfn, '/home/data/blah.txt')

return?

Answer 1

[dpb]

There's an inconsistency here...

K>> testdata.fullfn
ans = '/home/data/blah.txt'

shows the single quotes around the content which indicates that the variable is a cell string but ischar then should've returned false instead.

To prove conjecture, try

fid = fopen(char(testdata.fullfn), 'r')

I'm guessing there's a context issue between the two cases above where there are different variables extant of the same name but in different scopes.

ADDENDUM

Or, possibly the variable is a character string but has the single quotes embedded in it if was constructed incorrectly...

>> test = '''/home/data/blah.txt''';
>> test
test =
'/home/data/blah.txt'
>> ischar(test)
ans =
   1
>>

Produces all the symptoms consistently in that is character string, output "looks like" a cell string but fopen will fail because the filename won't match with the added quotes.

[Stephen23]

The last explanation matches the description perfectly:

>> str = '''blah.m'''
str = 'blah.m'
>> [fid,msg] = fopen(str,'rt')
fid =
    -1
msg =
No such file or directory
>> new = eval(str);
>> [fid,msg] = fopen(new,'rt')
fid =
     3
msg =
     ''