strange behavior with fopen
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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!
2 个评论
Steven Lord
2017-1-13
Call fopen with two output arguments and show us what the contents of the second output are when fopen returns -1.
Guillaume
2017-1-13
and what does
strcmp(testdata.fullfn, '/home/data/blah.txt')
return?
回答（1 个）
dpb
2017-1-14
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.
1 个评论
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 =
''
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