Fstream infinite loop while reading file in C ++
I am in class CS101 at my school using C ++. I have a program that needs to read a file in this format:
Ramirez, Manny
1572838992 a 4 b 5 x 4 a 7 c 3 c 4 *
Kemp, Matt
3337474858 a 4 b 4 b 4 a 4 *
It is supposed to read the file, calculate the GPA of each student, and output the student's name, ID, units, and GPA. For a while, I tried different things several times and I went back and forth with endless loops. I got help from a friend who I had some stuff.
I've tried changing the loop condition inside the while (! Eof) loop so many times that I cannot count them all. Every time I look at what to do online, the advice I get is just not to use it yet! Eof because it has a penchant for creating infinite loops. Well, I know this now, but my professor wants us to do this.
Here is my code:
#include <iostream>
#include <fstream>
#include <string>
#include <iomanip>
#include <sstream>
using namespace std;
int main() {
char grade;
int units=0, studentsGrade=0, studentUnits=0;
int unitTotal=0;
float gradeTotal=0, gpa = 0;
string inputName, outputName, fullName;
long ID;
ifstream inputFile;
ofstream outputFile;
cout << "Please enter the input filename: ";
cin >> inputName;
cout << "Please enter the output filename: ";
cin >> outputName;
inputFile.open(inputName.c_str());
if (inputFile.fail())
cout << "Bad input file name." << endl;
else {
outputFile.open(outputName.c_str());
outputFile << left << setw(25) << "Name" << setw(15) << "ID" << setw(15)
<< "Units" << setw(15) << "GPA" << endl;
outputFile << "--------------------------------------------------------------------------------" << endl;
cout << left << setw(25) << "Name" << setw(15) << "ID" << setw(15)
<< "Units" << setw(15) << "GPA" << endl;
cout << "--------------------------------------------------------------------------------" << endl;
getline(inputFile, fullName);
while (!inputFile.eof()) {
gpa = 0;
unitTotal = 0;
gradeTotal = 0;
inputFile >> ID;
outputFile << setw(25) << fullName;
outputFile << setw(15) << ID;
cout << setw(25) << fullName << setw(15) << ID;
string line;
getline(inputFile,line);
istringstream iss(line);
while (!iss.eof()) {
units = 0;
iss >> grade >> units;
if (grade == '*')
break;
if (units > 0 && units <=5 && (grade == 'a' || grade == 'A')) {
gradeTotal += 4 * units;
studentsGrade += 4 * units;
unitTotal += units;
studentUnits += units;}
else if (units > 0 && units <=5 && (grade == 'b' || grade == 'B')) {
gradeTotal += 3 * units;
studentsGrade += 3 * units;
unitTotal += units;
studentUnits += units; }
else if (units > 0 && units <=5 && (grade == 'c' || grade == 'C')) {
gradeTotal += 2 * units;
studentsGrade += 2 * units;
unitTotal += units;
studentUnits += units; }
else if (units > 0 && units <=5 && (grade == 'd' || grade == 'D')) {
gradeTotal += 1 * units;
studentsGrade += 1 * units;
unitTotal += units;
studentUnits += units; }
else if (units > 0 && units <=5 && (grade == 'f' || grade == 'F')) {
unitTotal += units;
studentUnits += units; }
else if (grade == '*') {
unitTotal += 0;}
else {
unitTotal += 0; }
}
gpa = (float)gradeTotal / unitTotal;
outputFile << fixed << showpoint;
outputFile << setw(15) << unitTotal << setw(15) << setprecision(2) << gpa << endl;
cout << fixed << showpoint;
cout << setw(15) << unitTotal << setw(15) << setprecision(2) << gpa << endl;
getline(inputFile,fullName);
}
outputFile << "The GPA for all students is " << setprecision(2) << (float)studentsGrade / studentUnits;
cout << "The GPA for all students is " << setprecision(2) << (float)studentsGrade / studentUnits << endl;
}
inputFile.close();
outputFile.close();
cout << endl;
return 0;
}
If anyone can explain to me why I keep getting an infinite loop, I would really appreciate it.
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While this needs to be verified by running the code, it seems that you get failbit
either badbit
, but not eof
. This can happen, for example, after other readings, and not getline()
- for example inputFile >> ID;
.
Since you are only checking eof
, the loop runs indefinitely and I / O errors are ignored. I would try using the result getline()
and use operator void*
for std::istream
instead of checking eof()
.
If your professor only wants you to use eof()
, then try a workaround error checking. The solution might be to use special values and assume that if the read operation did not set a value for something else, then it failed and exited the loop. For example, set ID
in before reading LONG_MAX
and make sure it is not LONG_MAX
after.
Finally - just run the code under the debugger on a small working dataset, go over and see what happens. Get to know yourself with a debugger and learn troubleshooting skills. This will surely save you a lot of time throughout your career.
See also - http://www.cplusplus.com/reference/iostream/ifstream/
Good luck!
Checking for eof is not enough. You also need to check the result of your read functions, at least at critical points, such as after reading a value. For example, there may be a space at the end of the file. You can test if (cout.fail())
for this.
Better if you can find a way to record the part that starts here:
if (units > 0 && units <=5 && (grade == 'a' || grade == 'A')) {
like a loop with a body like this:
gradeTotal += i * units;
studentsGrade += i * units;
unitTotal += units;
studentUnits += units;
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