Convert stream bytes to string

Question

I am using google protocol buffers to send some data from a C++ server to a IOS app. I use this function on the IOS side to convert the stream bytes to a string:

-(NSString*)convertStreamBytesToString:(NSMutableData*)data
{
    int len = [data length];
    char raw[len];

    [data getBytes:raw length:len];
    NSString *protocStruct =[[NSString alloc] initWithBytes:raw length:len encoding:NSUTF8StringEncoding];

    return protocStruct;

}

My problem is that sometimes this doesn't work. I can see that I send and receive all the bytes, but when converting some of them are lost. So for example I get 83 bytes, but when printing the string I get about 20 characters. Where are the rest ? Is there a problem I don't know about this converting method ?

Answer 1

NSString is a class for handling Unicode strings. You cannot store arbitrary bytes in it as with a C string. (And even then you probably cannot transmit binary data in place of a character string and expect it to survive the transport)

You will need to convert your binary data to a string in a way that results in a valid text string. For example via Base64 encoding.

There are lots of iOS projects you can get to encode/decode Base64, just google it.

Here's an article about it: http://www.cocoawithlove.com/2009/06/base64-encoding-options-on-mac-and.html?m=1

Answer 2

Allocating C array on stack in obj-c causes error sometimes. Try to use dynamic memory for char array:

char* raw = (char*)malloc(len*sizeof(char));

And free it afterwards:

free(raw);