std::string_view (C++17)

Non-owning, read-only string references

The Problem

Before C++17, passing strings to functions required choosing between const char* (no size), const std::string& (requires conversion), or std::string (copies).

// Old ways: problematic
void process_cstr(const char* str);     // No size info
void process_string(const std::string& s);  // Requires std::string

// Problems:
process_string("hello");  // Creates temporary std::string

// std::string_view solves this
#include <string_view>

void process(std::string_view sv);  // Works with all string types

// Usage - no allocations!
process("hello");                    // C string literal
process(std::string("hello"));       // std::string
process(some_string_view);           // Another string_view

Key Features

std::string_view sv = "Hello, World!";

// O(1) operations
size_t len = sv.size();     // Length
bool empty = sv.empty();    // Check if empty
char c = sv[0];             // Index access (no bounds check)
char safe = sv.at(0);       // Safe access with bounds check

// Creating subviews - O(1), no copy
auto sub = sv.substr(0, 5);  // "Hello"

// Compare
if (sv == "Hello, World!") { }

// Find
size_t pos = sv.find("World");

Best Practices

  • ✓Use std::string_view for read-only string parameters
  • ✓Pass by value (cheap to copy, like a pointer + size)
  • ✗Never store string_view as member variable (dangling risk)
  • ✗Don't use after the source string has been destroyed