In iOS development, is it possible to use NSString and return it from a function?
e.g.
(NSString * ) foo {
return @"";
}
This is not an objective c method, just function
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1Yes, you can, but you don't do it like that...Richard J. Ross III– Richard J. Ross III2012-08-30 11:53:37 +00:00Commented Aug 30, 2012 at 11:53
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1Please learn C before Objective-C. You don't even know the syntax for a C function...user529758– user5297582012-08-30 11:54:05 +00:00Commented Aug 30, 2012 at 11:54
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4 Answers
Yes, seeing as objective-c objects are just pointers, you can create a C function to return one:
NS_RETURNS_RETAINED NSString *myFunction() {
return [[NSString alloc] init];
}
Notice the use of NS_RETURNS_RETAINED. This is a hint to ARC and the static analyzer that this function returns a retained value to the receiver, and that it's their responsibility to release it.
If you were returning an autoreleased value, try using NS_RETURNS_NOT_RETAINED instead.
answered Aug 30, 2012 at 11:55
Richard J. Ross III
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7 Comments
Richard J. Ross III
@H2CO3 Not necessarily true. With objective-c 2.5 (what I call the addition of the new literals), a NSString literal is not guaranteed to be a constant (e.g. allocated in the executable's memory). It could very well be allocated on the heap at run-time, you don't know.
Ryan
@RichardJ.RossIII Do you mean if I have
alloc init in the return than I should use NS_RETURNS_RETAINED, and if I return @"xxx" then I should use NS_RETURNS_NOT_RETAINED? What if I don't provide the hints (Assume I am using ARC already)Richard J. Ross III
@Yoga if you don't provide hints, then for all methods that aren't
alloc and init, NS_RETURNS_NOT_RETAINED is the default. |
Yes, but the syntax is different:
NSString *foo()
{
return @"bar";
}
13 Comments
Hot Licks
And, of course, the file must be a an
m or mm file or have it's file type attribute set appropriately in Info.Richard J. Ross III
@HotLicks no, it's completely valid to have a C-function in a header file as long as it is defined as
static, so that you don't run into linker errors. In fact, it's quite common to have a static inline C function in a header, such as NSMakeRange.Richard J. Ross III
@H2CO3 I agree. In fact, there are excellent 3rd party alternatives to Xcode, such as AppCode by JetBrains (but it costs a fortune). And nothing beats the command line compiler.
Hot Licks
@RichardJ.RossIII -- The point is that, without the right file type, the file will be compiled as C and the the
@ will be a syntax error. |
NSString *foo()
{
const char* yourString = "bar";
NSString* yourNSString = [NSString stringWithFormat:@"%s", yourString];
return yourNSString;
}
4 Comments
Richard J. Ross III
Yes, it's a way to return a NSString from a C function, but it's not how you create a NSString from a C-string. Try using
+stringWithUTF8String: instead.Richard J. Ross III
@H2CO3 if your C-string is NULL, then you have other issues to worry about most likely.
Yes, why not? Check NSStringFromRect() and similar for a reference.
