I have a file that contains a list of books. Each book has 4 variables delimitated by a Tab.
The variables are
- Title
- author
- isbn
- qty
and there are around 400 book entries.
I have managed to write a function that reads each input to an array and saves it to a Book object.
void loadFile() {
std::ifstream inputFile("books");
std::string bookArray[4];
std::string line;
Book book;
while (getline(inputFile, line)) {
size_t field2 = 0;
size_t field1 = line.find("\t");
for (int i = 0; i <= 3; i ) {
size_t field1 = line.find("\t" , field2);
if (field1 != std::string::npos) {
std::string str2 = line.substr(field2, field1 - field2);
bookArray[i] = str2;
}
field2 = field1 1;
}
book.setTitle(bookArray[0]);
book.setAuthor(bookArray[1]);
book.setIsbn(bookArray[2]);
book.setQty(stoi(bookArray[3]));
std::cout << "Book: " <<book.getTitle <<'\t'<< book.getQty<< " records.\n";
}
but the function seems to not pick up the qty numbers at the end of each line. Everything else seems to be fine except the qty numbers. I cant find what's wrong with the function.
I have tried implementing the same getline() function with a '\t' delimitator argument like so:
while(getline(input, line, '\t')) {
The output just read the title of the first line and stopped there. I know the first function works.
Why is it not picking up the qty values?
The books file format is as follows:
A First Look at Graph Theory Clark John; Holton Derek Allan 9788170234630 5
A Practical Approach To Data Structures And Algorithms Sanjay Pahuja 9788122420678 7
A Practical Approach to High-Performance Computing Sergei Kurgalin; Sergei Borzunov 9783030275587 6
A Practical Guide to UNIX for Mac OS X Users Mark G. Sobell; Peter Seebach 9780321629982 5
A River Marc Martin 9781452162256 4
Total Noob here so I apologize if my code is awkward.
CodePudding user response：
The reason is that there's (likely) no tab character at the end of the line after the qty. So when you call line.find("\t", field2) the 4th time, it returns string::npos and you don't store anything in bookArray[3]
The best fix is probably to put an else there with the if:
} else {
std::string str2 = line.substr(field2, std::string::npos);
bookArray[i] = str2;
break; // there can be no more fields on the line
be aware that if you have a line with fewer than 4 fields, the elements of bookArray for the unfound fields will not be touched (so will continue to have values from the previous line)
CodePudding user response：
Chris Dodd's answer explains why your code is failing to parse the qty values.
As an alternative solution, I would suggest using a std::istringstream to parse each line with std::getline(), let it handle the searching and splitting for you 1, eg:
void loadFile() {
std::ifstream inputFile("books");
std::string bookArray[4];
std::string line;
Book book;
while (std::getline(inputFile, line)) {
std::istringstream iss(line);
for(int i = 0; i < 4; i) {
std::getline(iss, bookArray[i], '\t');
}
book.setTitle(bookArray[0]);
book.setAuthor(bookArray[1]);
book.setIsbn(bookArray[2]);
book.setQty(stoi(bookArray[3]));
std::cout << "Book: " << book.getTitle << '\t' << book.getQty << " records.\n";
}
}
1: there are, of course, many different ways to tokenize a string on a delimiter.
Alternatively, let the istringstream handle the conversion of the qty to an int for you, no need to call std::stoi() manually:
void loadFile() {
std::ifstream inputFile("books");
std::string bookArray[3];
int qty;
std::string line;
Book book;
while (std::getline(inputFile, line)) {
std::istringstream iss(line);
for(int i = 0; i < 3; i) {
std::getline(iss, bookArray[i], '\t');
}
iss >> qty;
book.setTitle(bookArray[0]);
book.setAuthor(bookArray[1]);
book.setIsbn(bookArray[2]);
book.setQty(qty);
std::cout << "Book: " << book.getTitle << '\t' << book.getQty << " records.\n";
}
}