How to convert an NSData to const char *?

Question

I am trying to convert a NSData object with audio data to a const char *. I have to do this because the API I am trying to call expects const char *. But I am unable to do so as

const char * stream = [data bytes]; //won't compile

also

const char * stream = (const char *)[data bytes];

will compile but will only have the first 2 bytes for some reason.

Thanks in advance.

Answer 1

const char* is assumed to point at a null-terminated string, so the first null character in the NSData object will terminate the string.

Performing this conversion using a cast does not make sense out of context, since it's just asking the API to interpret an NSData as a const char* .

If you are trying to pass an NSData to an API that wants const char* , you are likely to be using the wrong API for your purpose, or you need to re-encode your data before using the API.

Update: Based on the OP's comment, he wants to encode the data to decode it later.

There are a variety of different solutions for this, but one simple possibility is to base64 encode the data using the API method . You could then base64 decode it using the symmmetric API method . You could then convert the resulting NSString to const char* using the approach suggested in this answer .

Answer 2

Assuming the NSData you are loading is originally a string, you can try something like this:

NSString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
const char *chars = [string UTF8String];

This will first convert the NSData to a NSString, and then convert the NSString to const char pointer.

Update

Since you are trying to just encode the data as a hex string, take a look at this thread:

How to convert an NSData into an NSString Hex string?

It should look something like this:

NSUInteger capacity = data.length * 2;
NSMutableString *sbuf = [NSMutableString stringWithCapacity:capacity];
const unsigned char *buf = data.bytes;
NSInteger i;
for (i=0; i<data.length; ++i)
{
  [sbuf appendFormat:@"%02X", (NSUInteger)buf[i]];
}
const char *chars = [sbuf UTF8String];