How to Convert int to String in C++: Complete Guide

The most common methods to convert integers to strings in C++ include std::to_string() (C++11 and later), stringstream operations, itoa(), sprintf(), and boost::lexical_cast. Each approach offers different trade-offs in terms of performance, readability, portability, and C++ standard compliance.

• Getting Started with Integer to String Conversion
• Comparison of Conversion Methods
• Performance Analysis
• Best Practices and Recommendations
• Advanced Techniques and Edge Cases

Getting Started with Integer to String Conversion

Method 1: Using itoa()

The itoa() function is a C-style conversion method that converts an integer to a null-terminated string. However, it’s not part of the C++ standard library and has some limitations.

int a = 10;
char buffer[32]; // Ensure sufficient buffer size
itoa(a, buffer, 10); // 10 is the radix (base)
string str = string(buffer);

Pros:

• Simple and straightforward syntax
• Fast execution
• Works with all integer types

Cons:

• Not standard C++ (part of C standard library)
• Buffer size management required
• Not type-safe
• Limited error handling

According to the C++ FAQ, itoa() is generally discouraged in favor of standard C++ solutions.

Method 2: Using stringstream

Stringstreams provide a C+±style approach for type conversions through stream operations.

int a = 10;
stringstream ss;
ss << a;
string str = ss.str();

Pros:

• Part of standard C++ library
• Type-safe
• Works with all numeric types
• Flexible formatting options

Cons:

• Relatively slow performance
• More verbose syntax
• Requires including <sstream>

As noted in cppreference.com, stringstream operations are convenient but can be inefficient for simple conversions.

Comparison of Conversion Methods

Method 3: Using std::to_string() (C++11 and later)

This is the most straightforward and recommended approach in modern C++.

int a = 10;
string str = to_string(a);

Pros:

• Simplest syntax
• Standard C++ (since C++11)
• Type-safe
• Works with all integer types (int, long, long long, etc.)
• No buffer management needed

Cons:

• Requires C++11 or later

The C++ Standard Library documentation confirms that std::to_string() is the preferred method for basic integer-to-string conversions in modern C++.

Method 4: Using boost::lexical_cast

For projects using the Boost library, lexical_cast provides a convenient conversion mechanism.

#include <boost/lexical_cast.hpp>
int a = 10;
string str = boost::lexical_cast<string>(a);

Pros:

• Consistent syntax for all type conversions
• Handles error cases
• Works with various types

Cons:

• Requires Boost library
• Slight performance overhead
• Overkill for simple integer conversions

Method 5: Using sprintf/snprintf

These C-style functions offer formatting control but require manual buffer management.

int a = 10;
char buffer[32];
snprintf(buffer, sizeof(buffer), "%d", a);
string str = string(buffer);

Pros:

• Full formatting control
• Standard C/C++
• Good performance

Cons:

• Manual buffer management
• Error-prone with buffer sizes
• More complex syntax

Method 6: Using string Constructors with Iterators

For advanced use cases, you can use string constructors with numeric iterators.

int a = 10;
string str;
str += to_string(a); // Combines with other operations

Pros:

• Flexible for complex scenarios
• Can be combined with other string operations

Cons:

• More complex syntax
• Not the most efficient for simple conversions

Performance Analysis

Benchmark Results

Based on performance testing across different compilers and platforms:

Key Findings:

• std::to_string() consistently performs best in modern C++
• Stringstream operations are significantly slower due to stream overhead
• itoa() and snprintf() offer competitive performance but lack standard C++ guarantees

According to performance benchmarks on Stack Overflow, std::to_string() is the optimal choice for both performance and readability in C++11 and later.

Best Practices and Recommendations

Modern C++ Approach (C++11 and later)

For any new C++ project, prefer std::to_string():

int number = 42;
string result = to_string(number);

Why it’s best:

• Standard library guarantee
• Type-safe
• Simple syntax
• Good performance
• No external dependencies

Legacy Code Considerations

For older C++ code (pre-C++11) or systems without C++11 support:

// For pre-C++11 code
stringstream ss;
ss << number;
string result = ss.str();

Error Handling Considerations

When working with potentially problematic conversions:

try {
    string result = to_string(number);
    // Use result
} catch (...) {
    // Handle potential exceptions
}

Advanced Techniques and Edge Cases

Custom Formatting

For specific formatting requirements:

#include <iomanip>
stringstream ss;
ss << setw(5) << setfill('0') << number;
string result = ss.str();

Large Number Handling

For very large integers:

long long bigNumber = 123456789012345LL;
string result = to_string(bigNumber);

Cross-Platform Considerations

For maximum portability:

// Works on all platforms with C++11
int number = 123;
string result = to_string(number);

Sources

1. C++ Standard Library - std::to_string
2. C++ FAQ - String Conversion
3. cppreference.com - String Streams
4. Stack Overflow - Integer to String Performance
5. Boost Library Documentation - lexical_cast
6. C++ String Conversion Guide

Conclusion

For modern C++ development, std::to_string() is the recommended approach for converting integers to strings due to its simplicity, performance, and standard library support. If you’re working with C++11 or later, this should be your default choice.

Key recommendations:

• Use std::to_string() for simple, efficient conversions in C++11+
• Reserve stringstream operations for complex formatting needs
• Avoid itoa() unless working with legacy C code or specific constraints
• Consider boost::lexical_cast only if you’re already using Boost libraries
• Always handle potential exceptions when converting user input

For most practical applications, the choice between methods comes down to your C++ standard version, performance requirements, and project dependencies. The modern C++ approach with std::to_string() offers the best balance of performance, readability, and maintainability.