On Nov 23, 2008, at 11:56 AM, Kevin Gessner wrote:
Rather than hitting the file system every time you want to check file existence, you could cache it from -[NSFileManager directoryContentsAtPath:]. You could run in to a race condition (if another process creates a file between when you check the list and when you write your file), but that's true of your iterative solution as well.
This is a good idea, but you do need to be careful. For instance, the following program reports this:
froude:tmp amaxwell$ cc -o nametest -framework Foundation nametest.m froude:tmp amaxwell$ ./nametest 2008-11-23 12:32:40.408 nametest[2186:10b] created Test File2008-11-23 12:32:40.411 nametest[2186:10b] contentsOfDirectoryAtPath contains Test File 2008-11-23 12:32:40.412 nametest[2186:10b] fileExistsAtPath: says that Test File exists
2008-11-23 12:32:40.412 nametest[2186:10b] created Test file2008-11-23 12:32:40.413 nametest[2186:10b] contentsOfDirectoryAtPath does not contain Test file 2008-11-23 12:32:40.413 nametest[2186:10b] fileExistsAtPath: says that Test file exists
froude:tmp amaxwell$ ll Test\ File -rw-r--r-- 1 amaxwell wheel 0 Nov 23 12:32 Test File"Test File" exists, but checking contentsOfDirectoryAtPath: and fileExistsAtPath: for the existence of "Test file" gives contradictory results.
In some respects, it would be nice if the array returned by NSFileManager used case-insensitive equality callbacks when called on a case-insensitive filesystem. Cocoa has a number of weird edge cases like this (e.g. instances of NSURL for files may not compare equal for the same file: URL, depending on how they were created).
--
Adam
#import <Foundation/Foundation.h>
int main (int argc, char const *argv[])
{
NSAutoreleasePool *pool = [NSAutoreleasePool new];
NSFileManager *fm = [NSFileManager defaultManager];
NSString *fname = @"Test File";
if ([fm createFileAtPath:fname contents:[NSData data]
attributes:nil])
NSLog(@"created %@", fname);
NSArray *content = [fm contentsOfDirectoryAtPath:[fm
currentDirectoryPath] error:NULL];
if ([content containsObject:fname])
NSLog(@"contentsOfDirectoryAtPath contains %@", fname);
else
NSLog(@"contentsOfDirectoryAtPath does not contain %@", fname);
if ([fm fileExistsAtPath:fname])
NSLog(@"fileExistsAtPath: says that %@ exists", fname);
else
NSLog(@"fileExistsAtPath: says that %@ does not exist", fname);
fname = @"Test file";
if ([fm createFileAtPath:fname contents:[NSData data]
attributes:nil])
NSLog(@"created %@", fname);
if ([content containsObject:fname])
NSLog(@"contentsOfDirectoryAtPath contains %@", fname);
else
NSLog(@"contentsOfDirectoryAtPath does not contain %@", fname);
if ([fm fileExistsAtPath:fname])
NSLog(@"fileExistsAtPath: says that %@ exists", fname);
else
NSLog(@"fileExistsAtPath: says that %@ does not exist", fname);
[pool release];
return 0;
}
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