Convert NSString into char array

Question

I have a variable of type char[] and I want to copy NSString value in it. How can I convert an NSString to a char array?

Answer 1

We need to play NSString as a character array for working on coding practices which is otherwise much simpler to do in plain C coding. Using characterAtIndex: and appendFormat: helps me. May be this will help.

NSString *str = @"abcdef";
NSMutableString *strResult = [NSMutableString string];

for (NSUInteger i = 0; i < [str length]; i++) {
  char ch = [str characterAtIndex:i];
  [strResult appendFormat:@"%c", ch];
}
NSLog(@"%@", strResult);

Answer 2

Use -[NSString UTF8String]:

NSString *s = @"Some string";
const char *c = [s UTF8String];

You could also use -[NSString cStringUsingEncoding:] if your string is encoded with something other than UTF-8.

---

Once you have the const char *, you can work with it similarly to an array of chars:

printf("%c\n", c[5]);

If you want to modify the string, make a copy:

char *cpy = calloc([s length]+1, 1);
strncpy(cpy, c, [s length]);
// Do stuff with cpy
free(cpy);

Answer 3

mipadi's answer is the best if you just want a char* containing the contents of the string, however NSString provides methods for obtaining the data into a buffer that you have allocated yourself. For example, you can copy the characters into an array of unichar using getCharacters:range: like this:

NSUInteger length = [str length];
unichar buffer[length];

[str getCharacters:buffer range:NSMakeRange(0, length)];

for (NSUInteger i = 0; i < length; i++)
{
    doSomethingWithThis(buffer[i]);
}

If you have to use char, then you can use the more complicated getBytes:maxLength:usedLength:encoding:options:range:remainingRange: like this (demonstrated in Eastern Polish Christmas Tree notation):

NSUInteger length = [str length];
NSUInteger bufferSize = 500;

char buffer[bufferSize] = {0};

[str       getBytes:buffer
          maxLength:(bufferSize - 1)
         usedLength:NULL
           encoding:NSUTF8StringEncoding
            options:0
              range:NSMakeRange(0, length)
     remainingRange:NULL];

Answer 4

Rather than getCharacters:range:, I use:

[stringToCopy getCString:c_buffer maxLength:c_buffer_length encoding:NSUTF8StringEncoding];

The result is a char[] (instead of unichar[]), which is what the OP was wanting, and what you probably want to use for C compatibility.

Answer 5

NSMutableArray *array = [NSMutableArray array];
for (int i = 0; i < [string length]; i++) {
    [array addObject:[NSString stringWithFormat:@"%C", [string characterAtIndex:i]]];
}

Answer 6

In Swift, a char array is bridged as an UnsafePointer<Int8>. Accessing characters works the same way in Swift for an NSString:

let str: NSString = "hello"
let charStr = str.UTF8String // UnsafePointer<Int8>

For a Swift String object things are a little different:

let str = "hello"
let charStr = str.cStringUsingEncoding(NSUTF8StringEncoding)

charStr is [CChar]? where CChar is a typeailais for Int8.