Correct syntax for fopen in C?

Completely Clueless · 10-23-2009, 09:13 AM

Hi guys,

Is this scource code snippet correct?

fp=fopen("/home/Desktop/documents/test.txt","r");

I'd have thought these forward slashes in the pathname in this context need to be escaped, do they not?

I mean like this:

fp=fopen("//home//Desktop//documents//test.txt","r");

Which is correct?

Thanks. cc.

JohnGraham · 10-23-2009, 09:30 AM

Quote:

Originally Posted by Completely Clueless

Hi guys,

Is this scource code snippet correct?

fp=fopen("/home/Desktop/documents/test.txt","r");

I'd have thought these forward slashes in the pathname in this context need to be escaped, do they not?

I mean like this:

fp=fopen("//home//Desktop//documents//test.txt","r");

Which is correct?

Thanks. cc.

The fist one will work - the '/' character does not need to be escaped. As it happens, the second one will also work, since multiple '/'-s get treated as one (or maybe as an implicit '/./', I'm not sure, but I don't think it makes any difference). From a shell, try e.g. `ls /path/to/file' and `ls //path////to////////////////file'. This is useful because you don't have to worry about e.g. string1 + '/' + string2 concatenating to make '/path///to/file'.

John G

theNbomr · 10-23-2009, 10:16 AM

While JohnGraham does touch on the matter, I think it worth pointing out explicitly that the question seems to involve two levels of translation of '/'s. On one level, the C compiler must translate the literal string from its source code form to the runtime character array. It does so according to one or more rules. The second level of translation is at the filesystem/OS level, where the description of a filespec is derived from a string. In this case, a completely different set of rules may apply, and would be independent of the programming language.
To answer the question "Is this scource code snippet correct?", there is no definitive answer except, perhaps, "It depends...".

--- rod.

tuxdev · 10-23-2009, 10:36 AM

If you want to have consistent behaviour across both Windows and Linux, use "rb" mode. If you use just "r", Windows will translate CRLF into LF for you.. which is generally not good for cross-platform reliability.

Completely Clueless · 10-23-2009, 11:20 AM

Quote:

Originally Posted by theNbomr

While JohnGraham does touch on the matter, I think it worth pointing out explicitly that the question seems to involve two levels of translation of '/'s. On one level, the C compiler must translate the literal string from its source code form to the runtime character array. It does so according to one or more rules. The second level of translation is at the filesystem/OS level, where the description of a filespec is derived from a string. In this case, a completely different set of rules may apply, and would be independent of the programming language.
--- rod.

Okay, thanks all. Fully understood.

Sergei Steshenko · 10-23-2009, 11:21 AM

Quote:

Originally Posted by Completely Clueless

Hi guys,

Is this scource code snippet correct?

fp=fopen("/home/Desktop/documents/test.txt","r");

I'd have thought these forward slashes in the pathname in this context need to be escaped, do they not?

I mean like this:

fp=fopen("//home//Desktop//documents//test.txt","r");

Which is correct?

Thanks. cc.

Under Windows you would have to write something like

Code:

fp=fopen("C:\\User\\Desktop\\documents\\test.txt","r");

- backslashes, not forward slashes, need escaping.

Actually, you'd have to escape backslashes under Linux too, just under Linux backslashes are just regular characters in a file path, they are not path elements separators.

OTOH, Windows accept forward slash as path separator.