no suitable conversion function from (C++) std::istream &std::getline, std::allocator> to bool

Question

I've tried the types string and char with no success.

First post sorry if I did anything incorrectly.

if (inputFile.is_open())
{
    bool data = getline(inputFile, line, '$');
    while (data)
    {
        name = line;
        getline(inputFile, course, '$');
        getline(inputFile, line, '$');
        clearGrading = line == "1" ? true : false;
        getline(inputFile, line, '$');
        goodFeedback = line == "1" ? true : false;
        getline(inputFile, line, '$');
        caring = line == "1" ? true : false;
        getline(inputFile, line, '$');
        reachable = line == "1" ? true : false;
        getline(inputFile, line, '$');
        toughGrader = line == "1" ? true : false;
        getline(inputFile, line, '$');
        lectureHeavy = line == "1" ? true : false;
        getline(inputFile, line, '$');
        attendance = line == "1" ? true : false;
        data = getline(inputFile, line, '$');

Welcome to Stack Overflow! Please post your code as text, not images. For people that can't see images for one reason or another your question is unanswerable. — NathanOliver, Dec 07 '20 at 19:20
image of program when run https://imgur.com/gallery/zCIATHj and File being read https://imgur.com/gallery/FAxrbtb — Toby Aderounmu, Dec 07 '20 at 19:22
Don't write code like this: `clearGrading = line == "1" ? true : false;`. Just say: `clearGrading = (line == "1");` — selbie, Dec 07 '20 at 19:28

score 0 · Answer 1 · edited Dec 07 '20 at 19:54

This code:

bool data = getline(inputFile, line, '$');
while (data)
{

The return value of getline() is not a bool, it's the original input stream (the first param to getline()) - likely such chaining can be done or so that it can be invoked in a loop

Easy fix is simply this:

while (getline(inputFile, line, '$'))
{

Two other issues. Don't have code that explicitly converts a boolean expression to true/false. Just let the boolean expression be itself.

Instead of this:

caring = line == "1" ? true : false;

This:

caring = (line == "1");

Finally, I would recommend you check the stream state after every call to getline(). You aren't doing that consistently. That is, instead of this:

name = line;
getline(inputFile, course, '$');
getline(inputFile, line, '$');

Do this:

name = line;
if (inputfile)
    getline(inputFile, course, '$');
if (inputfile)
    getline(inputFile, line, '$');

_"or so that it can be invoked in a loop"_ Yeah, via conversion to bool... — Asteroids With Wings, Dec 07 '20 at 19:53

score 0 · Answer 2 · answered Dec 07 '20 at 20:01

std::getline() returns a reference to the input istream it is given. The stream has a bool conversion operator defined to test the stream state in a boolean context. However, since C++11, that operator is marked as explicit, which means it can't be used to initialize a bool variable without an explicit type-cast, eg:

bool data = (bool) getline(inputFile, line, '$');

Or:

bool data = static_cast<bool>(getline(inputFile, line, '$'));

However, explicit operators are allowed to be used without type-cast in certain contexts, which includes while statements (see When can I use explicit operator bool without a cast?), eg:

while (getline(inputFile, line, '$'))

no suitable conversion function from (C++) std::istream &std::getline, std::allocator> to bool

2 Answers2