How to Insert into String in C++: Syntax and Examples

In C++, you can insert text into a string using the insert() method, which allows you to specify the position and the text to add. For example, str.insert(pos, "text") inserts "text" at the index pos in the string str.

Syntax

The insert() method in C++ strings lets you add characters or another string at a specific position.

• str.insert(pos, s): Inserts string s starting at index pos.
• pos: The zero-based index where insertion begins.
• s: The string or characters to insert.

cpp

string& insert (size_t pos, const string& str);

Example

This example shows how to insert a substring into a string at a specific position.

cpp

#include <iostream>
#include <string>

int main() {
    std::string str = "Hello World!";
    str.insert(6, "Beautiful ");
    std::cout << str << std::endl;
    return 0;
}

Output

Hello Beautiful World!

Common Pitfalls

Common mistakes when using insert() include:

• Using an invalid position (greater than string length), which causes an exception.
• Forgetting that string indices start at 0.
• Trying to insert into a const string (which is not allowed).

cpp

#include <iostream>
#include <string>

int main() {
    std::string str = "Hello";
    // Wrong: position out of range
    // str.insert(10, "World"); // This will throw std::out_of_range

    // Correct usage:
    str.insert(5, " World");
    std::cout << str << std::endl;
    return 0;
}

Output

Hello World

Quick Reference

Remember these tips when inserting into strings:

• Positions start at 0.
• Position must be less than or equal to string length.
• insert() modifies the original string.
• You can insert single characters or whole strings.

Key Takeaways

Use insert(pos, text) to add text at a specific position in a C++ string.

Ensure the position is within the string length to avoid errors.

String indices start at zero, so count carefully.

insert() changes the original string directly.

You can insert both single characters and strings using insert().