Question

What’s the safest way for a NSString to weakly contain a const char * belonging to a std::string? Both examples below work on a simple test, in logs, and as presented in a NSTableView, but I’m concerned about strange behavior down to road. It may be the extra null character of c_str() is simply ignored (because of the length parameter passed) and either will work fine.

Given:

std::string const * stdstring = new std::string("Let's see if this works");

Then:

NSString * aStr = [[NSString alloc] initWithBytesNoCopy: 
    stdstring->data() length: stdstring->length() 
    encoding:NSUTF8StringEncoding  freeWhenDone:NO];

or:

NSString * aStr2 = [[NSString alloc] initWithBytesNoCopy: 
    stdstring->c_str() length: stdstring->length() 
     encoding:NSUTF8StringEncoding  freeWhenDone:NO];

or something else?

Answer 1

The documentation for initWithBytesNoCopy:length:... clearly states that the length will be the number of bytes used, so the null termination character will always be ignored. Hence the contents of the memory returned by data() and c_str() is equally suitable.

With that in mind:

The lifetime guarantees of the memory returned by std::string‘s data() and c_str() functions are identical – they will survive until you call a non-const member function on the string object. It depends on the implementation whether the internal data structure is already a null-terminated character array, so in general, data() will be cheaper or identical in complexity to c_str(). I’d therefore go for data().