C++ string vs string_view: Fast, Non-Owning String Handling (C++17)

Character sequences are a form of resizable array; the same asymptotic picture as arrays and lists often applies to heavy concatenation loops.

Introduction: “My string-heavy code is slow"

"If I pass std::string by value, does it copy?”

std::string_view (C++17) references character data without copying. Using it for read-only parameters removes many allocations/copies.

void print(std::string s);            // may copy
void print(std::string_view s);       // cheap view

This article covers:

• string vs string_view
• Benchmarks
• Parameter guidelines
• Lifetime pitfalls
• Patterns

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Table of contents

1. Comparison
2. Benchmarks
3. Parameter selection
4. Pitfalls
5. Patterns
6. Summary

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1. string vs string_view

Table

Aspect	std::string	std::string_view
Ownership	Owns buffer (typically heap)	Non-owning view
Copy cost	Can allocate + copy	Pointer + size copy
Mutation	Yes	No
Size	Implementation-defined	Usually 16 bytes
Null termination	c_str() is NTBS	Not guaranteed by data() alone
Lifetime	Managed by string object	Must outlive the view

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2. Benchmarks

Passing std::string by value vs std::string_view vs const std::string& often shows large wins for by-value string parameters in hot loops.

substr: string_view::substr avoids allocating a new string when you only need a view.

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3. Parameter selection

Need	Use
Read-only text	std::string_view
Mutate in place	std::string&
Store owned text	std::string member
C API needing NTBS	std::string then c_str()

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4. Pitfalls

Dangling views

Do not return a string_view to characters owned by a local std::string that is destroyed.

Not necessarily null-terminated

Do not pass sv.data() to APIs expecting a C string unless you know it is null-terminated or use std::string(sv).c_str().

Temporary string

Binding a string_view to a temporary std::string without extending lifetime is a classic bug.

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5. Patterns

• Parsing/tokenizing with views to avoid substring allocations.
• Logging APIs taking string_view, storing logs as std::string when needed.

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Summary

• Read-only parameters: prefer string_view.
• Owned storage: std::string.
• Never let a view outlive the underlying characters.

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Related reading

• C++ string_view guide
• C++ STL string
• C++ any

Keywords

string vs string_view, C++17, no-copy strings, substring performance

Practical tips

• Replace by-value std::string parameters with string_view where semantics allow.
• Use sanitizers to catch use-after-free style mistakes with views.

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Related posts

• C++ string (complete)
• C++ any