string at() in C++

std::string::at can be used to extract characters by characters from a given string.

It supports two different syntaxes both having similar parameters:
Syntax 1:

char& string::at (size_type idx)

Syntax 2:

const char& string::at (size_type idx) const

idx : index number
Both forms return the character that has the index idx (the first character has index 0).
For all strings, an index greater than or equal to length() as value is invalid.
If the caller ensures that the index is valid, she can use operator [], which is faster.

Return value : Returns character at the specified position in the string.

Exception : Passing an invalid index (less than 0 
or greater than or equal to size()) throws an out_of_range exception.
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// CPP code to demonstrate std::string::at
  
#include <iostream>
using namespace std;
  
// Function to demonstarte std::string::at
void atDemo(string str)
{
    cout << str.at(5);
  
    // Below line throws out of
    // range exception as 16 > length()
    // cout << str.at(16);
}
  
// Driver code
int main()
{
    string str("GeeksForGeeks");
    atDemo(str);
    return 0;
}

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Output:

F

Application



std::string::at can be used for extracting characters from string. Here is the simple code for the same.

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// CPP code to extract characters from a given string
  
#include <iostream>
using namespace std;
  
// Function to demonstarte std::string::at
void extractChar(string str)
{
    char ch;
  
    // Calculating the length of string
    int l = str.length();
    for (int i = 0; i < l; i++) {
        ch = str.at(i);
        cout << ch << " ";
    }
}
  
// Driver code
int main()
{
    string str("GeeksForGeeks");
    extractChar(str);
    return 0;
}

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Output:

G e e k s F o r G e e k s 

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