How to number input in ascending order? - c++

Question

I have input coming in form a file input.txt as two columns of strings such as:
string1 string2
string3 string4
etc.
I am trying to number the strings in ascending order starting form 0 but in such a way that repeating strings don't get assigned new values but keep the once already assigned to them.
I decided to use a set::find operation to do this, but I am having a hard time making it work. Here's what I have so far:
int main(int argc, char* argv[]) {
std::ifstream myfile ("input.txt");
std::string line;
int num = 0; // num is the total number of input strings
if (myfile.is_open()) {
while(std::getline(myfile, line)) {
++num;
}
}
std::string str1, str1; // strings form input
int str1Num, str2Num; // numbers assigned to strings
int i = 0; // used to assign values to strings
StringInt si;
std::vector<StringInt> saveStringInts(num);
std::set<std::string> alreadyCounted(num, 0);
std::set<std::string>::iterator sit;
std::ifstream myfile2 ("input.txt");
if (myfile2.is_open()) {
while(myfile2.good()) {
// read in input, put it in vars below
myfile2 >> str1 >> str2;
// if strings are not already assigned numbers, assign them
if ((*(sit = alreadyCounted.find(str1)).compare(str1) != 0) { // doesn't work
str1Num = i++;
alreadyCounted.insert(str1);
saveStringInts.push_back(StringInt(str1Num));
}
else {
str1Num = si->getNum(str1);
}
if ((*(sit = alreadyCounted.find(str2)).compare(str2) != 0) {
str2Num = i++;
alreadyCounted.insert(str2);
saveStringInts.push_back(StringInt(str2Num));
}
else {
str2Num = si->getNum(str2);
}
// use str1 and str2 in the functions below before the next iteration
}
}
Unfortunately, I tried other approaches and now completely stuck. If you know how to fix my code or can suggest a better way to accomplish my task, I would greatly appreciate your help.

Answer 1

You need to compare std::set<int>::iterator against the end() iterator of your set, rather than dereferencing the iterator and comparing its value against something! Actually, derferencing the end() iterator is undefined behavior:
if ((*(sit = alreadyCounted.find(str1)).compare(str1) != 0) // WRONG: don't do that!
should really be
if (alreadyCounted.find(str1) != alreadyCounted.end())
... and likewise for the other string. Personally, I would use a different technique, though: when insert()ing into a std::set<T>, you get back a pair of an iterator and an indicator whether the object was inserted. The latter together with the current set's size give the next value, e.g.:
bool result = alreadyCounted.insert(str1).second;
strNum1 = result? alreadyCounted.size() - 1: si->getNum(str1);