Question

For any function that is declared to take a char* output parameter, is there a way to specify the “char” part of s std::string as the function’s output?

I began with:

// EDIT:  ADDED THESE TWO LINES FOR CLARITY

sprintf(buf, "top -n 1 -p %s" , commaSeparatedListOfPIDs.c_str() );
fp = popen(buf, "r");

std::string  replyStr;
char         reply[100];

rc = scanf( fp, "%s", reply );
replyStr = reply;

but that seems a bit, well, clumsy.

So, is there a way to say:

rc = scanf( fp, "%s", &replyStr.c_str() );

or something like that?

Thanks!

Answer 1

Yes this is possible:

std::string  replyStr(100, '\0');
//Requires C++11 (to guarantee that strings hold their characters
//in contiguous memory), and some way to ensure that the string in the file
//is less than 100 characters long.
rc = fscanf( fp, "%s", &reply.front() );
replyStr.erase(replyStr.find('\0'));

The second condition is very difficult to satisfy, and if it is not satisfied this program has undefined behaviour.