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How do you convert between std::string and numbers?

Beginner

Answer

Use std::to_string(n) to convert numbers to strings, and std::stoi/std::stol/std::stod etc. to parse strings to numbers. C++17 adds std::from_chars/std::to_chars for fast, locale-independent, non-throwing conversions ideal for performance-critical parsing.
std::string s = std::to_string(42);
int n = std::stoi("123");
// fast: std::from_chars(begin, end, value);
Real-world example A CSV parser uses std::from_chars for fast, allocation-free numeric parsing.

Common follow-ups: What does stoi do on invalid input? | Why prefer from_chars for performance?

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