C++ Compare and replace last character of stringstream - c++

Question

I would like to check the following:
If the last character appended to the stringstream is a comma.
If it is remove it.
std::stringstream str;
str << "["
//loop which adds several strings separated by commas
str.seekp(-1, str.cur); // this is to remove the last comma before closing bracket
str<< "]";
The problem is if nothing is added in the loop, the opening bracket is removed from the string. So I need a way to check whether the last character is a comma. I did that like this:
if (str.str().substr(str.str().length() - 1) == ",")
{
str.seekp(-1, rteStr.cur);
}
But I don't feel very good about this. Is there a better way to do this?
About the loop:
Loop is used to tokenize a set of commands received through sockets and format it to send to another program through another socket. Each command ends with an OVER flag.
std::regex tok_pat("[^\\[\\\",\\]]+");
std::sregex_token_iterator tok_it(command.begin(), command.end(), tok_pat);
std::sregex_token_iterator tok_end;
std::string baseStr = tok_end == ++tok_it ? "" : std::string(*tok_it);
while (baseStr == "OVER")
{
//extract command parameters
str << "extracted_parameters" << ","
}

Answer 1

The way I often deal with these loops where you want to put something like a space or a comma between a list of items is like this:
int main()
{
// initially the separator is empty
auto sep = "";
for(int i = 0; i < 5; ++i)
{
std::cout << sep << i;
sep = ", "; // make the separator a comma after first item
}
}
Output:
0, 1, 2, 3, 4
If you want to make it more speed efficient you can output the first item using an if() before entering the loop to output the rest of the items like this:
int main()
{
int n;
std::cin >> n;
int i = 0;
if(i < n) // check for no output
std::cout << i;
for(++i; i < n; ++i) // rest of the output (if any)
std::cout << ", " << i; // separate these
}
In your situation the first solution could work like this:
std::regex tok_pat("[^\\[\\\",\\]]+");
std::sregex_token_iterator tok_it(command.begin(), command.end(), tok_pat);
std::sregex_token_iterator tok_end;
std::string baseStr = tok_end == ++tok_it ? "" : std::string(*tok_it);
auto sep = ""; // empty separator for first item
while (baseStr == "OVER")
{
// extract command parameters
str << sep << "extracted_parameters";
sep = ","; // make it a comma after first item
}
And the second (possibly more time efficient) solution:
std::regex tok_pat("[^\\[\\\",\\]]+");
std::sregex_token_iterator tok_it(command.begin(), command.end(), tok_pat);
std::sregex_token_iterator tok_end;
std::string baseStr = tok_end == ++tok_it ? "" : std::string(*tok_it);
if (baseStr == "OVER")
{
// extract command parameters
str << "extracted_parameters";
}
while (baseStr == "OVER")
{
// extract command parameters
str << "," << "extracted_parameters"; // add a comma after first item
}