CODEWITHSUNDEEP
c++stringstringstream
Kiran
Kiran

Reputation: 5526

use a string or stream?

I need to progressively build a string and am trying to find the best way to do it. The maximum it can grow to is about 10k and hence was planning to do something like this:

const unsigned long long configSize = 10240; //Approximation
void makeMyConfig() {
   std::string resp;
   std::string input;
   resp.reserve(configSize);
   while ( getInput(input) ) {
     resp += input;
   }

   if ( resp.length > configSize ) 
      log << "May need to adjust configSize. Validate" << endl;

   if (!sendConfig(resp)){
      log << "Error sending config" << endl;
   }
}

getInput may read from file/tcp conn or ftp and is decided at runtime. It receives const char* and puts it into a string (which I may be able to avoid but left it for convenience)

However, I heard there is a much efficient way of doing with string streams but not sure how to do. Appreciate any insights.

Upvotes: 2

Views: 304

Answers (2)

user2100815
user2100815

Reputation:

For anyone interested in the difference between reserving and not reserving a string, consider this code:

#include <iostream>
#include <string>
#include <ctime>
using namespace std;

const int BIG = 10000000;
const int EXTRA = 100;

int main() {

    string s1;
    s1.reserve( BIG );

    clock_t t = clock();
    for ( int i = 0; i < BIG + EXTRA; i++ ) {
        s1 += 'x';
    }
    cout << clock() - t << endl;

    string s2;
    t = clock();
    for ( int i = 0; i < BIG + EXTRA; i++ ) {
        s2 += 'x';
    }
    cout << clock() - t << endl;
}

In the first case, the string is reserved, in the second not. This produces the timings:

60
78

for g++ compiled with -O2.

Upvotes: 0

Graham Perks
Graham Perks

Reputation: 23398

Looks pretty great to me.

  • You're pre-allocating the buffer, avoiding ongoing allocations and copies.
  • You already have it implemented

Don't optimize until you actually have a performance problem and can measure any performance changes. You might end up making it worse without realizing!

Upvotes: 13

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