Converting C function to C++ language - c++

Question

Since this is my first encounter with the C programming language, it's not clear to me how I'm going to convert a piece of code to C++. I know that this code can be used in C ++ but I want to work exclusively on the syntax of the C++ language.
Here is my code:
FILE *f;
char name[10],surname[10],j[10];
f=fopen("Marks.txt","r");
fscanf(f,"%d",&n);
I want to open the file using:
ifstream input;
input.open("Marks.txt");
But then I don't know what to use instead of the fscanf function because I can no longer use FILE *f;

Answer 1

Like this:
int main()
{
// Let the constructor handle opening the file.
std::ifstream input("Marks.txt");
int n = 0;
std::string s;
double d = 0;
// Read an int, followed by a string, followed by a double.
if (input >> n >> s >> d)
{
std::cout << "Success!\n";
}
else
{
std::cout << "Failure!\n";
}
// The destruction of 'input' will close the file.
}

Answer 2

Here's the C++ way to do it, though you technically can still use that C code.
#include <ifstream>
int main() {
std::string str;
int i;
double d;
char c_str[10];
std::ifstream input;
input.open("Marks.txt");
input >> str; // reads a word of text into str
input >> i; // assuming there is a valid integer after the first line, reads it into i
input >> d; // assuming there is a valid double after that, reads it into d
// reads up to 9 characters + a '\0', stopping if it reaches a period
input.get(c_str, 10-1, '.');
// etc.
}

Answer 3

First to do is make a std::fstream object then open the file of your choice, you can do any lines (in sequence) of the following:
// Option 1
std::fstream input; // create the object
input.open("Marks.txt", ios::in); // since this is a `std::fstream` object, you'll need to specify `ios::in` for input operations
// Option 2
std::ifstream input; // create the object, this time dedicated to input
input.open("Marks.txt"); // no need to specify `ios::in`
// Option 3
std::fstream input("Marks.txt", ios::in); // you can directly open the file using the constructor, but specify `ios::in`
// Option 4
std::ifstream input("Marks.txt"); // directly opening the file using the constructor with the object dedicated to input
Next, you'll use operator>> or std::getline() to get input from the stream
// first declare the variables
std::string str1 = ""; // use std::string in C++ instead C-style strings (char[])
int ing1 = 0;
// Option 1
input >> str1; // this parses the contents of the file into str1, until the space
/*
Suppose "Marks.txt" has this inside it:
Hello World
The first content of the file until a space is "Hello", this string parsed into str1
*/
// Option 2
ing1 = input.get() // this parses only one character then turns it into an integer (destination type) into ing1
/*
Suppose "Marks.txt" has this inside it:
1234567890
ing1 will bear the value 1.
however, like std::iostream, this does not convert the character to it's integral value (ASCII, automatically) thus when:
abcdefghij
ing1 will have the value 0, since 'a' is not an integer
*/
// Option 3
input.getline(str1, 6); // this will parse into str1 six (6) characters, including spaces (not sure with control characters)
/*
Suppose "Marks.txt" has this inside it:
StackOverflow
"StackO" will be parsed into str1
*/
Note: this operations differ when stream is opened in binary mode (ios::binary) and be careful with std::getline() this may overload the buffer (especially when specified with std::numeric_limits<std::streamsize>::max())
EDIT: IMPORTANT close the stream after using.
// some operations here
// file is no longer needed -> close it
input.close();