Why am I hitting string subscript out of range?

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I get string subscript out of range error by running these code.

C++

int main() {

	//Read file
	string filename = "";
	std::cout << "Welcome to the Bank system!\n";
	std::cout << "Please input the file name of the data file: ";
	std::cin >> filename;
	ifstream myfile(filename);
	
	int i = 0; // number of char
	int j = 0; // number of column
	int k = 0; // number of ac
	char c = 'a';
	bool skip = false;
	string temp = "";
	string pwhold;
	string amounthold;
	string acnohold;
	string telnohold;
	string namehold;
	if (myfile.is_open()) {
		while (getline(myfile, temp)) {
			pwhold = "";
			amounthold = "";
			acnohold = "";
			telnohold = "";
			namehold = "";
			j = 0;
			skip = false;
			i = 0;	
			while (!skip) {
				char c = temp[i];
				if (c == '\n') {
					skip = true;
					break;
				}
				else if (c == '\t') {	
					j++;
				}
				else {
					switch (j) {
					case 0: acnohold = acnohold + c; break;
					case 1: namehold = namehold + c; break;
					case 2: telnohold = telnohold + c; break;
					case 3: pwhold = pwhold + c; break;
					case 4: amounthold = amounthold + c; break;
					default: break;
					}
				}
				i++;
			}	
			system("pause");
			temp = " ";
			db1[k].pw = stoul(pwhold, nullptr, 0);
			db1[k].deposit = stod(amounthold, nullptr);
			db1[k].telno = stoul(telnohold, nullptr, 0);
			db1[k].acno = stoul(acnohold, nullptr, 0);
			db1[k].name = namehold;
			k++;
		}
	}

The textfile used:

567123456	Chan Tai Man	90112233	3942681528	1234.56
567112233	Wong Mei Lai	60123456	2670544664	10000.12
567555555	Lau Tak Wah	69876543	3418631757	888888.88
567987654	Wong Siu Ming	60123456	3752537240	1300000.12

Why will the problem happen and how do I fix it?

What I have tried:

I have tried google the answer but still...

Posted 30-Nov-19 5:05am

Yeungpok Pyin

Updated 30-Nov-19 7:03am

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4 solutions

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CPallini · Answer 1 · 2019-11-30T07:03:00

Quote:
if (c == '\n') {
skip = true;
break;
}

The above condition is never satisfied, because getline discards the newline character.
(See std::getline - cppreference.com[^]: "b) the next available input character is delim, as tested by Traits::eq(c, delim), in which case the delimiter character is extracted from input, but is not appended to str").
Change to:

C++

if (i >= temp.size()) {
         skip = true;
         break;
       }

Please note, you might also
either

change the std::cin field delimiter (in order to use the TAB character), see, for instance: stream - changing the delimiter for cin (c++) - Stack Overflow[^].

or

Use regular expressions, see regex[^].

OriginalGriff · Answer 2 · 2019-11-30T05:17:00

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

C#

int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

Patrice T · Answer 3 · 2019-11-30T05:31:00

Quote:
Why am I hitting string subscript out of range?

What happen if a line do not end with a \n ?

Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your code is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

The downside of this solution:
- It is a DIY, you are the one tracking the problem and finding its roots, which lead to the solution.
The upside of this solution:
- It is also a great learning tool because it show you reality and you can see which expectation match reality.

secondary effects
- Your will be proud of finding bugs yourself.
- Your learning skills will improve.

You should find pretty quickly what is wrong.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]

1.11 — Debugging your program (stepping and breakpoints) | Learn C++[^]

The debugger is here to only show you what your code is doing and your task is to compare with what it should do.

Rick York · Answer 4 · 2019-11-30T06:43:00

A subscript out of range error means an array index has exceeded its allowed range. I would guess it is from accessing db1 but I can't be certain since your code does not include its declaration.

I recommend using a vector for db1 and its push_back method and you won't have to worry about it any more, if you can.

Why am I hitting string subscript out of range?

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