输出文件流的“<<”和“put()”之间的区别

Question

I am trying to understand the difference between the '<<' operator and the 'put()' function for writing characters to an output file.

My code:

#include <fstream>
using namespace std;

int main() {
    ofstream out ("output.txt");

    int x = 1;

    // This produces the incorrect result ...
    out.put(x);
    
    // ... while this produces the correct result
    out << x;


    // These two produce the same (correct) result
    out.put('a');
    out << 'a';
    
    out.close;
}

I get that out.put(x) converts the integer 1 into a character according ASCII code, but I don't understand why this doesn't happen when I use out << x .

However, out.put('a') does produce the same as out << 'a' .

Why is this?

Answer 1

当您使用out << 1 ，您调用： operator<<(int val)而不是： operator<<(char val) ，然后他可以将int为std::string 。

Answer 2

int x = 1;

// This produces the incorrect result ...
out.put(x);

No, it converts the int to a char and outputs one char , with the value 1 .

// ... while this produces the correct result
out << x;

That does formatted output and outputs the the representation of the value x holds. Most probably it'll show the character 1 which is different from the character with value 1 .

// These two produce the same (correct) result
out.put('a');
out << 'a';

Yes, there's no conversion there. Had you done

int x = 'A';
out.put(x);
out << x;

You'd probably see A65 where A comes from the put(x) and 65 from the formatted output since 65 is often the value of 'A' .