c++ moving to next element in a file.txt [duplicate]

Answer 1

When reading in from a file as you are doing, all data is seen as a string. You must check to see if the string is a number. Here is a way to convert a string to an integer (IF THAT STRING IS AN INTEGER): atoi() function Be careful though, you must pass it a c-string.

Answer 2

You can do the following

int num = 0;
while(myfile >> num || !myfile.eof()) {
    if(myfile.fail()) { // Number input failed, skip the word
        myfile.clear();
        string dummy;
        myfile >> dummy;
        continue;
    }
    cout << num << endl; // Do whatever necessary with the next number read
}

See a complete, working sample here

Answer 3

You can get the all data as a string and try convert the data to an integer in a try {} catch () { } block. If the data is real an integer, perform the operation in try section, else if code go to the catch and don't do any operation in catch.

Answer 4

Oops it's already solved. But worth to mention, there is also possibility to:

• either read individual chars from the stream and pushback() if they are digits before using operator >>

• or peek() the next chars in the stream without reading it to decisde whether to ignore it or to use operator >>

Just be carefull about the '-' which is not a digit but could be the sign of an interger.

Here a small example :

int c, n, sign=1; 
ifstream ifs("test.txt", std::ifstream::in);

while (ifs.good() && (c=ifs.peek())!=EOF ) {
    if (isdigit(c)) {
        ifs >> n;
        n *= sign; 
        sign = 1; 
        cout << n << endl; 
    }
    else {
        c=ifs.get();
        if (c == '-')
            sign = -1;
        else sign = 1;
    }
}
ifs.close(); 

It's not the most performant approach, however it has the advantage of only reading from stream, without intermediary strings and memory management.