Int from string from redirected input C++

[PirateMcplunder]

Hello!

I am working on some code which is eventually supposed to simulate (very primitively) packed fragmentation and reassembly in a transparent network. Unfortunately, I can't seem to read in the input correctly.

The puzzling thing to me is that I have some code where I seem to be able to read in the first integer on the first line correctly (num_hops) but I can't read in subsequent integers with essentially the same code!!

Any help, suggestions, tips, pointers or hints would be greatly appreciated.

An example of the input is as follows:

2 #number of hops
35 # maximum payload size for hop 1
20 # maximum payload size for hop 2
27 0 0 "This is the payload, whi"
27 24 0 "ch may span multiple lin"
27 48 1 "es until end of input."

As you can see, the pound signs are convenient delimiters. I am trying to use getline to grab each line of input (all of which is redirected from a file as standard input) and then I am trying to use getline again with a delimiter to chop the line up. Finally, I am trying to use streams to get the first part of the string (which should just be an int) into a variable of type int.

Why does this work the first time and not subsequently?


#include <iostream>
#include <sstream>
#include <string>
#include <stdio.h>
using namespace std;

int main () {

int num_hops; /* number of hops within hypothetical network */
string first_input_line;
string* max_payload_lines; /* placeholder for array of strings, containing input lines with maximum payload values. The count of these lines should be = to the number of hops */
int* max_payloads; /* placeholder for array of integers, containing the maximum payload values themselves. The count of these values should be = to the number of hops */
string* restof_input_lines; /* string array for the remaining lines of input (i.e. packet/payload lines) */
string before_token; /* buffer for string before delimiting token */
string after_token; /* buffer for string after delimiting token */
stringstream input_buffer; /* stringstream for reading input from stdin */
stringstream conversion_buffer; /* stringstream for variable assignment */
size_t found; /* flag for checking references to appropriate fields when input lines are scanned for expected descriptors in their comments */

/* Usage */
string usage = "Usage:\np2 < testfile\n\nWhere testfile is the name of a field containing input data in the following format\n2 #number of hops\n35 # maximum payload size for hop 1\n20 # maximum payload size for hop 2\n27 0 0 \"This is the payload, whi\"\n27 24 0 \"ch may span multiple lin\"\n27 48 1 \"es until end of input.\"";

/* interpret initial input */

/* get first line */
if(!getline(cin, first_input_line)){
cerr << "Getline failure. Are you sure you redirected input?!" << endl;
cerr << usage << endl;
}

input_buffer << first_input_line;

found=first_input_line.find("number of hops"); /* check first line for reference to the number of hops. */
if (found==string::npos){
cerr << "No explicit reference to \"number of hops\" found in the comment for first input line." << endl;
cerr << usage << endl;
exit(1);
}

getline(input_buffer, before_token, '#'); /* get first input line up to token "#", set value for num_hops */
cout << before_token << endl;
conversion_buffer << before_token;
conversion_buffer >> num_hops;

/* clear values of buffers, string placeholders and flags for future reuse */
found = 0;
input_buffer.clear(stringstream::goodbit);
conversion_buffer.clear(stringstream::goodbit);
before_token = "";
after_token = "";
/* now we know the number of hops and therefore the number of maximum payload lines to expect */

/* get lines containing maximum payloads for each hop */
max_payloads = new int[num_hops]; /* initialize and zero array of ints for stroing maximum payload values to the size of the number of hops */
for (int i = 0 ; i < num_hops ; i ++){
max_payloads[i] = 0;
}

max_payload_lines = new string[num_hops]; /* initialize array of strings for stroing maximum payload line comments to the size of the number of hops */

for(int j = 0 ; j < num_hops ; j++){
if(!getline(cin, max_payload_lines[j])){
cerr << "Getline failure. Are you sure you redirected input correctly?!" << endl;
cerr << usage << endl;
exit(2);
}

input_buffer << max_payload_lines[j];

found=max_payload_lines[j].find("maximum payload size"); /* search line for comment pertaining to maximum payload size */
if (found==string::npos){
cerr << "No explicit reference to \"maximum payload size\" found in the comment for input line #" << j << "\nAre you sure that you entered input correctly?" << endl;
cerr << usage << endl;
exit(3);
}

getline(input_buffer, before_token, '#'); /* get next input line pertaining to maximum payload size up to token "#", set value for num_hops */
cout << before_token << endl;
conversion_buffer << before_token;
conversion_buffer >> max_payloads[j]; /* set maxmimum payload for this hop */

/* clear values of buffers, string placeholders and flags for future reuse */
found = 0;
input_buffer.clear(stringstream::goodbit);
conversion_buffer.clear(stringstream::goodbit);
before_token = "";
after_token = "";
}

cout << num_hops << endl;
for (int k = 0 ; k < num_hops ; k++)
{
cout << max_payloads[k] << endl;
cout << max_payload_lines[k] << endl;
}

/* now we have the number of hops and the maximum payload for each hop. it's time to read in the input packets! */
}


Thank you for your time and for your help!

[PirateMcplunder]

I've been looking for hours and I think I've identified the problem as having to do with the state of the stringstream (which would explain the working once and then breaking problem). I am using .clear after each use of the stringstreams, however; shouldn't this reset their state?

[PirateMcplunder]

Current output is:
2
number of hops35
maximum payload size for hop 120
2
0
35 # maximum payload size for hop 1
0
20 # maximum payload size for hop 2

where:
the first 2 is the "before_token" string after the streams are used successfully the first time
and the second and third lines are the "before_token" string printed just after the second attempt at a similar process.

[PirateMcplunder]

The only answers I've been able to find for problems similar to my own is to clear the state of the streams with .clear, but I am doing this already...

see: http://www.velocityreviews.com/forums/t283927-istringstream-str-only-works-once.html

[PirateMcplunder]

SOLVED:

DUUUURRRRRRRRRRRRRRR.

I was reseting the state of the stream but not the values in the stream itself!

"input_buffer.clear();"
was not enough.

input_buffer.str("");
was needed.

another lesson learned (beyond this technical one about streams) is to be very liberal with the print statements when debugging. If I remember that, maybe I'll save myself some time next time!

hope this helps someone else out in the future.