cpp-tips

Introduction

This is the collection of snippets I found on internet or made by me.

Contents:

• Defer function
• Format like printf
• Runtime exception with format

Defer

• Requirement: C++11 or later.
• Source: pmttavaras's answer on stackoverflow.
• Modified to use move-semantic for true zero-overhead by me.

Deferred functions will be called at the end of the scope where they were declared, in last-in-first-out order. 

Snippet:

#include <memory>

struct defer_dummy {};
template<class F>
struct deferer
{
    F _f;
    deferer(F&& f) noexcept : _f(f) {}
    ~deferer() { _f(); }
};
template<class F>
inline deferer<F> operator*(defer_dummy, F&& f) noexcept { return deferer<F>(std::move(f)); }
#define DEFER_(LINE) zz_defer##LINE
#define DEFER(LINE) DEFER_(LINE)
#define defer auto DEFER(__LINE__) = defer_dummy{} *[&]()

Sample:

int main()
{
    defer{ printf("4\n"); };
    defer{ printf("3\n"); };

    {
        defer{ printf("1\n"); };
    }
    
    defer{ printf("2\n"); };
}

Format like printf

• Source: ifreilicht's answer on stackoverflow.
• Modified to be more efficient by me.

Snippet:

#include <cstdio>
#include <memory>
#include <stdexcept>
#include <string>

namespace nstd
{
    template<typename... Args>
    std::string format(const std::string& format, const Args&... args)
    {
        int size_s = std::snprintf(nullptr, 0, format.c_str(), args...);
        if (size_s < 0) throw std::runtime_error("Error during formatting");
        std::string ret(size_s, '\x00');
        std::snprintf(&ret[0], size_s + 1, format.c_str(), args...);
        return ret;
    }
}

Sample:

int main()
{
    std::cout << nstd::format("hello %s!\n", "lebaoworks");
}

Runtime exception with format

• Source: Me.
• Requirement: format

Snippet:

#include <stdexcept>
#include <string>

namespace nstd
{
    struct runtime_error : public std::runtime_error
    {
        template<typename... Args>
        runtime_error(const std::string& format, const Args&... args) :
            std::runtime_error(nstd::format(format, args...)) {}
    };
}

Sample:

int main()
{
    try
    {
        throw nstd::runtime_error("test except by %s", "lebaoworks");
    }
    catch (std::exception& e)
    {
        printf("Got exception: %s", e.what());
    }
}