Useful C++ Code Snippets
Simple Profiling
If you want to get statistical confidence, just use google benchmark https://github.com/google/benchmark. Otherwise, simple profiling can be done with chrono:
#include <chrono>
...
auto start = std::chrono::high_resolution_clock::now();
...
auto end = std::chrono::high_resolution_clock::now();
auto duration = std::chrono::duration_cast<std::chrono::milliseconds>(end - start);
std::cout << "Duration: " << duration.count() << "ms\n";
Transaction Pattern
Sometimes it’s useful to have transactional code block where we can undo/commit a block of operations. We can use C++ RAII to do this:
class Transaction
{
bool committed = false;
// state
public:
Transaction(/*some state*/) { ... }
~Transaction() { if (!committed) { /*undo operation*/ } }
void Commit() noexcept { committed = true; }
}
Example usage is parsing where we want to parse a sequence-of-token or not at all
void ParseSequence()
{
Transaction transaction(tokenizer);
if (!tokenizer.Next(TokenType::Comma))
return; // automatically revert any changes
if (!tokenizer.Next(TokenType::StringLiteral))
return // automatically revert any changes
transaction.Commit(); // all operations succeeded
}
Get or Create std::map, std::unordered_map
std::unordered_map<Key, Value> map;
auto [iter, newEntry] = map.emplace(key, Value{});
if (newEntry)
iter->second = Value();
String Format
template < typename... Args >
inline std::string StringFormat(const char *format, Args... args)
{
size_t size = std::snprintf(nullptr, 0, format, args...) + 1; // Extra space for '\0'
auto buf = std::make_unique< char[] >(size);
std::snprintf(buf.get(), size, format, args...);
return std::string(buf.get(), buf.get() + size - 1); // We don't want the '\0' inside
}
Printf tricks
Print the first n characters:
const char* pStr = "C Tips and Tricks.";
printf( "%.*s\n", 5, pStr); // This will print "C Tips"
Print n spaces:
printf("%*s", 5, ""); // This will print " "
Class member size and offset
struct MyStruct
{
int field0;
char field1;
};
sizeof( MyStruct::field0 )
offsetof( MyStruct, field0 )
Transferring ownership
std::unique_ptr<T> ptr;
...
using Storage = typename std::aligned_storage<sizeof(NonConstT), alignof(NonConstT)>::type;
std::unique_ptr<Storage> stPtr = std::make_unique<Storage>();
// Transfer ownership to correct unique_ptr type
ptr.reset( reinterpret_cast<T *>( stPtr.release() ) );