How do I check if a StringStream variable is empty/null?

Just a quick question here guys. I've been searching to no avail so far.

A bit more info here:

stringstream report_string;

report_string << "some string here...";

In my code itself are various conditions for assigning values to the report_string variable.

I'd like to check whether it was assigned a value or not.

Solution 1:

myStream.rdbuf()->in_avail() can be used to get the count of available characters ready to be read in from a stringstream, you can use that to check if your stringstream is "empty." I'm assuming you're not actually trying to check for the value null.

For example if you want to extract an int from a stringstream and then see if there were any left over characters (ie. non-numeric) you could check if myStream.rdbuf()->in_avail() == 0.

Is that something similar to what you're trying to do? I'm not sure if there's better ways but I've done this in the past and it's worked fine for me.

https://en.cppreference.com/w/cpp/io/basic_streambuf/in_avail

EDIT: I see you just updated your question as I posted.

Solution 2:

An easy check would be to see if the string content of the stream is empty or not:

#include<assert.h>
#include<sstream>

int main(){
std::stringstream report_string;
report_string << ""; // an empty strin g

//emptiness check of stringstream
assert(report_string.str().empty());
}

Solution 3:

This method is efficient and should work with output strings as well:

ostringstream report_string;

if (report_string.tellp() == 0) {
    // do something
}

Solution 4:

One way would be to check the size of the internal string and compare against zero. Note that this is different from myStream.rdbuf()->in_avail() as AusCBlock suggests; in_avail() can return a value different from the actual size of the stream (if, for example, the internal buffer is represented with multiple non-contiguous memory blocks). In particular, in_avail() can, in principle, return zero in non-empty buffers (it's possible that the stringbuf specification restricts this further; I have no checked in that much detail).

Solution 5:

Use eof() instead.

Sample Code:

stringstream report_string;
if ( !(report_string.eof()) ) 
    cout << "report_string EMPTY! \n";