casting NSInteger into NSString

问题:

I'm trying to make one string out of several different parts. This below is what i have right now. I don't get any errors in my code but as soon as i run this and do the event that triggers it i get EXC_BAD_ACCESS. Is there another way of casting this NSInteger into a NSString?

NSString *part1, *part2, *tempString;

NSInteger num1;
NSInteger num2;

part1=@"some";
part2=@"text";    

tempString = [NSString stringWithFormat:@"%@%@%@%@", 
              part1,
              (NSString *)num1, 
              part2, 
              (NSString *)num2];

回答1:

A string and an integer are fundamentally different data types, and casting in Objective-C won't do a conversion for you in this case, it'll just lie to the compiler about what's happening (so it compiles) but at runtime it blows up.

You can embed an integer directly into a format string by using %d instead of %@:

    tempString = [NSString stringWithFormat:@"%@%d%@%d", part1,num1, part2, num2];

---

NSInteger is just a fancy name for a regular "int" (number). An NSString is an object reference to a string object. Some numeric types (int and floating point) can be sort of converted between eachother directly in C like this, but these two aren't inter-operable at all. It sounds like you might be coming from a more permissive language? :)

回答2:

answered Feb 22 '12 at 22:34, Ben Zotto:

A string and an integer are fundamentally different data types, and casting in Objective-C won't do a conversion for you in this case, it'll just lie to the compiler about what's happening (so it compiles) but at runtime it blows up.

You can embed an integer directly into a format string by using %d instead of %@:

tempString = [NSString stringWithFormat:@"%@%d%@%d", part1,num1, part2, num2];

NSInteger is just a fancy name for a regular "int" (number). An NSString is an object reference to a string object. Some numeric types (int and floating point) can be sort of converted between eachother directly in C like this, but these two aren't inter-operable at all. It sounds like you might be coming from a more permissive language? :)

"Keep in mind that @"%d" will only work on 32 bit. Once you start using NSInteger for compatibility if you ever compile for a 64 bit platform, you should use @"%ld" as your format specifier." by Marc Charbonneau

So, solution:

tempString = [NSString stringWithFormat:@"%@%ld%@%ld", part1, (long)num1, part2, (long)num2];

Source: String Programming Guide for Cocoa - String Format Specifiers (Requires iPhone developer registration)

回答3:

You have to use %d for integer and not %@.

So, [NSString stringWithFormat:@"%@%d%@%d", part1,num1, part2, num2]; is the correct code to format your string.

Hope it helps.

回答4:

NSString* tempString = [NSString stringWithFormat:@"%@%d%d", part1, num1, num2];

回答5:

try the following:

 tempString = [NSString stringWithFormat:@"%@%d%@%d", part1,(NSString *)num1, part2, (NSString *)num2];

回答6:

NSIntegers are actual integers - not NSObject-derived objects. Try:

tempString = [NSString stringWithFormat:@"%@%d%@%d", part1, num1, part2, num2];

The cast trying to force NSInteger into NSString* is also dangerous, and probably the actual source of your crash. The compiler is letting you get away with it because it's trusting you know what you're doing with that kind of casting statement.

回答7:

NSString *part1, *part2, *tempString;

NSInteger num1;
NSInteger num2;

part1=@"some";
part2=@"text";

tempString = [NSString stringWithFormat:@"%@%d%@%d", part1,num1, part2, num2];
NSLog(@"%@",tempString);