stringf - printf to std::string

stringf.h

#ifndef STRING_INCLUDED_24298342934
#define STRING_INCLUDED_24298342934

#include <cstdio>
#include <string>
#include <cerrno>

// This file defines the function
//
//     std::string stringf(const char* format_string, args...)
//
// which works just like `printf` or `sprintf` except the result
// is returned in an `std::string`
// It also handles std::string arguments natively:
//
//     std::string ss("something");
//     stringf("Foo: %s", ss)
//
// Also defined is the macro
//
//     CSTRINGF(format_string, args..)
//
// Which is just `stringf().c_str()`

template <typename H, typename... Args>
std::string stringf(const char* s, const H& h, Args... args)
{
#ifndef _MSC_VER
#define SOME_SNPRINTF snprintf
#else
#define SOME_SNPRINTF _snprintf
#endif

    const size_t kBufsize = 4096;
    char buf[kBufsize];
    int r = SOME_SNPRINTF(buf, kBufsize, s, h, args...);

    if (0 <= r && r < kBufsize)
        return buf;

    errno = 0;

#ifdef _MSC_VER
    if (r < 0)
        r = _snprintf(0, 0, s, h, args...);
#endif

    if (r < 0)
        return "<SPRINTF ERROR>";

    std::vector<char> buf2(r + 1);
    buf2[0] = 0;
    SOME_SNPRINTF(buf2.data(), r + 1, s, h, args...);
    return buf2.data();

#undef SOME_SNPRINTF
}

template <typename... Args>
std::string stringf(const char* s, const std::string& ss, Args... args)
{
    return stringf(s, ss.c_str(), args...);
}

#define CSTRINGF(x, ...) (::sx::stringf(x, __VA_ARGS__).c_str())

#endif