72 lines
1.9 KiB
C++
72 lines
1.9 KiB
C++
#ifndef TEST_SUPPORT_FORMAT_STRING_H
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#define TEST_SUPPORT_FORMAT_STRING_H
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#include <cstdio>
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#include <string>
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#include <memory>
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#include <array>
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#include <cstdarg>
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namespace format_string_detail {
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inline std::string format_string_imp(const char* msg, ...) {
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// we might need a second shot at this, so pre-emptivly make a copy
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struct GuardVAList {
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va_list& xtarget;
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bool active;
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GuardVAList(va_list& val) : xtarget(val), active(true) {}
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void clear() {
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if (active)
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va_end(xtarget);
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active = false;
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}
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~GuardVAList() {
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if (active)
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va_end(xtarget);
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}
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};
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va_list args;
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va_start(args, msg);
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GuardVAList args_guard(args);
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va_list args_cp;
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va_copy(args_cp, args);
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GuardVAList args_copy_guard(args_cp);
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std::array<char, 256> local_buff;
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std::size_t size = local_buff.size();
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auto ret = ::vsnprintf(local_buff.data(), size, msg, args_cp);
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args_copy_guard.clear();
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// handle empty expansion
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if (ret == 0)
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return std::string{};
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if (static_cast<std::size_t>(ret) < size)
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return std::string(local_buff.data());
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// we did not provide a long enough buffer on our first attempt.
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// add 1 to size to account for null-byte in size cast to prevent overflow
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size = static_cast<std::size_t>(ret) + 1;
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auto buff_ptr = std::unique_ptr<char[]>(new char[size]);
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ret = ::vsnprintf(buff_ptr.get(), size, msg, args);
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return std::string(buff_ptr.get());
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}
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const char* unwrap(std::string& s) { return s.c_str(); }
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template <class Arg>
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Arg const& unwrap(Arg& a) {
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static_assert(!std::is_class<Arg>::value, "cannot pass class here");
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return a;
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}
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} // namespace format_string_detail
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template <class... Args>
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std::string format_string(const char* fmt, Args const&... args) {
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return format_string_detail::format_string_imp(
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fmt, format_string_detail::unwrap(const_cast<Args&>(args))...);
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}
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#endif // TEST_SUPPORT_FORMAT_STRING_HPP
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