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How to implement own function to read int?
By Qualified, history, 4 years ago, In English

I very much like $$$cin » $$$ but want to have this fast reading integers function. How to do it? For example, I want to input multiple integers in this $$$cin » a » b » c;$$$ but the reading of integers is using the comment above.

I tried this but it didn't work.

istream & operator >> (istream& os, int x) {
	bool minus = false;
	int result = 0;
	char ch;
	ch = getchar();
	while (true) {
		if (ch == '-') break;
		if (ch >= '0' && ch <= '9') break;
		ch = getchar();
	}
	if (ch == '-') minus = true; else result = ch-'0';
	while (true) {
		ch = getchar();
		if (ch < '0' || ch > '9') break;
		result = result*10 + (ch - '0');
	}
	if (minus)
		os >> -result;
	else
		os >> result;
	return os;
}

But I got this error

 error: ambiguous overload for 'operator>>' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'int')
  124 |   os >> result;
      |   ~~ ^~ ~~~~~~
      |   |     |
      |   |     int
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4 years ago, # |
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Auto comment: topic has been updated by Qualified (previous revision, new revision, compare).

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4 years ago, # |
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You cannot overload a previously declared function with the same arguments. The only way to create your own class.

The implementation looks like this. Not pretty, but it works.


#include <bits/stdc++.h>

using namespace std;

class custom_stream {
public:
    template<typename T> friend custom_stream & operator >> ( custom_stream &is, T &x ){
        std::cin >> x;
        return is;
    }
    friend custom_stream & operator >> ( custom_stream &is, int &x ){
        bool minus = false;
        int result = 0;
        char ch;
        ch = getchar();
        while( true ) {
            if ( ch == '-' ) break;
            if ( ch >= '0' && ch <= '9' ) break;
            ch = getchar();
        }
        if( ch == '-' ) minus = true; else result = ch-'0';
        while( true ) {
            ch = getchar();
            if ( ch < '0' || ch > '9' ) break;
            result = result*10 + (ch - '0');
        }
        if( minus )
            x = -result;
        else
            x = result;
        return is;
    }
};

#define cin in
custom_stream in;

int main()
{
    int n;
    cin >> n;
    cout << n << endl;
}
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