stringByAppendingPathComponent, hows it work?

Question

EDIT_v002

I have had a look at all the comments and I am starting to see what I should be doing. To that end I have modified my code (see below) I have changed newPath to a NSString, removed the [[alloc] init] and the end [release] as its now handled by the system. I am using stringByAppendingPathComponent, letting it add a separator between rootPath and fileName before its assigned to the NSString. It does work, and I ran it through the static analyser with no problems.

// ------------------------------------------------------------------- **
// DISC: FILEWALKER ..... (cocoa_fileWalker.m)
// DESC: List all "*.png" files in specified directory
// ------------------------------------------------------------------- **
#import <Foundation/Foundation.h>

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    NSString *fileName;
    NSDictionary *attrDir;
    NSError *myError;
    NSNumber *fileSize;
    NSFileManager *manager = [NSFileManager defaultManager];
    NSString *rootPath = [@"~/Pictures/Ren/PRMan" stringByExpandingTildeInPath];
    NSString *newPath;

    NSLog(@"Home: %@",rootPath);

    for(fileName in [manager enumeratorAtPath:rootPath]){
        if ([[fileName pathExtension] isEqual:@"png"]) {    

            newPath = [rootPath stringByAppendingPathComponent:fileName];   
            attrDir = [manager attributesOfItemAtPath:newPath error:&myError];
            fileSize = [attrDir objectForKey: @"NSFileSize"];
            NSLog(@"File: %@ Size: %@", newPath, fileSize);
        }
    }
    [pool drain];
    return 0;
}
// ------------------------------------------------------------------- **

gary

Answer 1

[testPath stringByAppendingString:@"/"]

Answer 2

You don't append the delimiter. You append the next path component (eg filename, dir, etc). This avoids you needing to know the delimiter for your particular system.

NSMutableString* mutablePath = [NSMutableString string];
NSString* fullPath = [rootPath stringByAppendingPathComponent:filename];

[mutablePath setString:fullPath]; // OK to setString: of Mutable with non-Mutable
[mutablePath appendString:someOtherString]; // This won't cause an exception

// Example to clarify on comments below
{
    // This will cause a compiler warning.
    // warning: incompatible Objective-C types assigning
    //    ‘struct NSString *’, expected ‘struct NSMutableString *’
    NSMutableString* ms = [@"FOO" stringByAppendingPathComponent:@"BAR"];
}

There is a fairly clear example in the documentation.

Answer 3

The last line should be:

testPath = [testPath stringByAppendingPathComponent:@"/"];

Answer 4

-stringByAppendingPathComponent returns a new immutable string, it doesn't modify the original. You have to use the return value of this method.

Answer 5

All the existing answers are leaking the original testPath string. For something as simple as this, why has nobody recommended -[NSMutableString appendString:] intead?

[testPath appendString:@"/"];

There's no equivalent to -stringByAppendingPathComponent: for NSMutableString, but it looks like he's just trying to add a slash, not a path component anyway. If you really wanted to add a path component, you could do this:

[testPath setString:[testPath stringByAppendingPathComponent:@"..."]];

It's an annoying workaround, but as @dreamlax points out, -stringByAppendingPathComponent: always returns an immutable string, even when called on an NSMutableString object. :-(

Answer 6

stringByAppendingPathComponent, hows it work?

Simple. You want to append a path component. You send that message to the string you want to append a path component to, passing the path component you want to append.

Path components are not the slashes; if they were, the pathComponents method would return nothing but an array of slashes. Path components are the parts between the slashes (although there is a special case, described in the definition of pathComponents).

The slash is the path separator. This is hard-coded inside of Cocoa; it's currently (and likely to always be) a slash. So, if you really wanted to append a slash to a string, the most likely reason would be that you want to append a path separator, not a path component.

    [newPath setString:rootPath];
    [newPath appendString:@"/"];
    [newPath appendString:fileName];

fileName is the component you want to add. Use stringByAppendingPathComponent: and pass fileName, not a slash.

As for whether your example leaks: Well, does an object fall out of scope without getting released? The answer to that question is the answer to whether it's a leak. If you're not sure, review the memory management rules.