function that returns a string

Question

Silly as it may sound, I am trying to write a simple function in objective-c which returns a string and displays it, the following code nearly works but I can't get printf to accept the functions return value ...

NSString* getXMLElementFromString();

int main(int argc, char *argv[])
{
    printf(getXMLElementFromString());
    return NSApplicationMain(argc,  (const char **) argv);
}

NSString* getXMLElementFromString() {
    NSString* returnValue;
    returnValue = @"Hello!";
    return returnValue;
}

fbrereto · Accepted Answer · 2009-08-21 18:44:36Z

5

NSString* is not equivalent to a traditional C string, which is what printf would expect. To use printf in such a way you'll need to leverage an NSString API to get a null-terminated string out of it:

printf("%s", [getXMLElementFromString() UTF8String]);

answered Aug 21, 2009 at 18:44

fbrereto

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1 Comment

Richard Smith Over a year ago

Thanks for helping, marvellous.

jbrennan · Accepted Answer · 2009-08-21 18:39:10Z

2

You should instead use NSLog() which takes a string (or a format string) as a parameter.

You could use either

NSLog(getXMLElementFromString());

or

NSLog(@"The string: %@", getXMLElementFromString());

Where the %@ token specifies an Objective-C object (in this case an NSString). NSLog() works essentially the same as printf() when it comes to format strings, only it will also accept the object token.

answered Aug 21, 2009 at 18:39

jbrennan

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1 Comment

Adam Rosenfield Over a year ago

The first form should almost always be avoided -- if an attacker can every specify a format string, you can get screwed over real fast.

Dave · Accepted Answer · 2009-08-21 18:38:24Z

1

I don't know that printf can handle an NSString. Try somethign like:

 printf ("%s\n", [getXMLElementFromString()cString]);

answered Aug 21, 2009 at 18:38

Dave

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2 Comments

jbrennan Over a year ago

I still would argue using NSLog() over printf() if you're going to be doing any serious Cocoa work.

Quinn Taylor Over a year ago

Prefer -UTF8String over -cString — check the NSString documentation.

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