Strings and I/O

String types

• std::string: owning text buffer
• std::string_view: non-owning view into text
• std::ostringstream, std::istringstream: stream-based formatting and parsing

Common operations

std::string name = "Ada";
name += " Lovelace";
auto pos = name.find("Love");
auto sub = name.substr(0, 3);

name.replace(0, 3, "Augusta");
bool has_prefix = name.starts_with("Aug");

These operations cover a lot of ordinary string work before you need regular expressions or custom parsers.

Input and output

int age{};
std::cout << "Enter age: ";
std::cin >> age;
std::cout << "Age = " << age << '\n';

Formatted extraction is good for token-oriented input. Use getline when spaces matter.

Line-based input

std::string line;
std::getline(std::cin, line);

std::istringstream input{"42 debug"};
int level{};
std::string tag;
input >> level >> tag;

String streams are useful when you want to parse one line at a time after reading it safely.

Safer text parameters

void greet(std::string_view name) {
    std::cout << "Hello, " << name << '\n';
}

Modern formatting

If available, prefer std::format over manual stream concatenation for complex output.

Best-practice reminders

• Use std::getline() when spaces matter.
• Use std::string_view only when the referenced data outlives the view.
• Be careful when mixing operator>> with std::getline().

std::string_view pitfalls

std::string_view bad_view() {
    return std::string{"temporary"};
}

Never return or store a view into a temporary string.

Modern formatting

auto text = std::format("{} scored {:.1f}%", name, percent);
std::print("Result: {}\n", text);

• std::format builds strings with Python-style format fields.
• std::print writes directly to standard output in C++23.

Parsing advice

• Prefer std::from_chars for fast numeric parsing in low-level code.
• Prefer std::getline plus parsing when you need robust line-oriented input.

Practical rule of thumb

• simple formatted tokens: >>
• full lines or user-entered text: getline
• structured formatting output: std::format or std::print
• low-allocation numeric parsing: std::from_chars