std::string_view is a lightweight class in C used to view existing string content, and does not copy or own memory. 1. Replace const std::string& as a function parameter to avoid copying; 2. Support efficient operations such as substr and find; 3. Pay attention to issues such as hanging references, non-modification, and literal length when using them; 4. Applicable to log parsing, performance-sensitive scenarios and general string processing functions.
Using C's std::string_view is actually quite simple. It's just that you "see" the string content without copying it. This is especially useful in handling large numbers of string operations or performance-sensitive scenarios.
What is std::string_view
Simply put, std::string_view is a lightweight string "view" that can point to an existing string (such as const char* or std::string ) but will not own it. You can understand it as a combination of pointer lengths, which makes it very efficient to access.
Common ways to use:
- As a function parameter, instead of
const std::string&to avoid unnecessary copying - Reduce memory allocation when processing string substrings, searching, comparison and other operations
How to use std::string_view to do basic operations
Declare and initialize:
std::string_view sv1 = "hello"; // Point to the literal std::string s = "world"; std::string_view sv2 = s; // Point to the content of string
Common methods:
-
sv.size()gets the length -
sv.empty()determines whether it is empty -
sv.data()gets the underlying character pointer -
sv.substr(pos, len)extracts substring -
sv.find("abc")find content location
For example, extract the domain name part in the URL:
std::string_view url = "https://example.com/path/to/resource";
auto start = url.find("://");
if (start != std::string_view::npos) {
url.remove_prefix(start 3); // Skip the protocol part}
auto slash_pos = url.find('/');
if (slash_pos != std::string_view::npos) {
url = url.substr(0, slash_pos); // Take out the domain name}
// Now url is example.com Notes on using std::string_view
Although it is easy to use, there are some pitfalls to pay attention to:
- Don't save it for too long: because
string_viewis just "looking" on other people's content, and if the original string is released, it becomes a dangling reference. - String literal default length problem: like
std::string_view sv = "hello", it will automatically recognize the length of 5 instead of\0that depends on the end. - Modification problem: You cannot modify the content of
string_viewdirectly, it is read-only (unless you cast it to a non-const pointer, but this is not recommended).
Suggestions for practical application scenarios
- Function parameters are passed : Use
std::string_viewinstead ofconst std::string&to improve efficiency. - Parsing logs, configurations, and text data : can be processed in segments without the need to frequently construct temporary strings.
- Key performance paths : such as network packet parsing and string matching algorithms, memory copy can be significantly reduced.
To give a practical example, write a general string prefix judgment function:
bool starts_with(std::string_view str, std::string_view prefix) {
return str.size() >= prefix.size() &&
str.substr(0, prefix.size()) == prefix;
} Basically that's it. std::string_view is small but practical. The key is to understand that it does not manage memory. Use the right place, the code is simpler and more efficient.
The above is the detailed content of C std::string_view tutorial. For more information, please follow other related articles on the PHP Chinese website!
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