Added zstring_span and removed zstring_builder to support legacy strings

include/string_span.h

@@ -71,17 +71,21 @@ namespace gsl
 // type system for these types that will not either incur significant runtime costs or
 // (sometimes needlessly) break existing programs when introduced.
 //
-template<std::ptrdiff_t Extent = dynamic_range>
-using czstring = const char*;
+
+template<typename CharT, std::ptrdiff_t Extent = dynamic_range>
+using basic_zstring = CharT*;
 
 template<std::ptrdiff_t Extent = dynamic_range>
-using cwzstring = const wchar_t*;
+using czstring = basic_zstring<const char, Extent>;
 
 template<std::ptrdiff_t Extent = dynamic_range>
-using zstring = char*;
+using cwzstring = basic_zstring<const wchar_t, Extent>;
 
 template<std::ptrdiff_t Extent = dynamic_range>
-using wzstring = wchar_t*;
+using zstring = basic_zstring<char, Extent>;
+
+template<std::ptrdiff_t Extent = dynamic_range>
+using wzstring = basic_zstring<wchar_t, Extent>;
 
 //
 // ensure_sentinel()
@@ -521,43 +525,56 @@ inline std::wstring to_string(wstring_span<> view)
 
 #endif
 
+// zero-terminated string span, used to convert
+// zero-terminated spans to legacy strings
 template<typename CharT, size_t Extent = dynamic_range>
-class basic_zstring_builder
+class basic_zstring_span
 {
 public:
-    using impl_type = span<CharT, Extent>;
-    using string_span_type = basic_string_span<CharT, Extent>;
     using value_type = CharT;
-    using pointer = CharT*;
-    using size_type = typename string_span_type::size_type;
-    using iterator = typename string_span_type::iterator;
+    using const_value_type = std::add_const_t<CharT>;
 
-    basic_zstring_builder(CharT* data, size_type length) : sv_(data, length) {}
+    using pointer = std::add_pointer_t<value_type>;
+    using const_pointer = std::add_pointer_t<const_value_type>;
 
-    template<size_t Size>
-    basic_zstring_builder(CharT(&arr)[Size]) : sv_(arr) {}
+    using zstring_type = basic_zstring<value_type, Extent>;
+    using const_zstring_type = basic_zstring<const_value_type, Extent>;
 
-    pointer data() const { return sv_.data(); }
-    string_span_type view() const { return sv_; }
+    using impl_type = span<value_type, Extent>;
+    using string_span_type = basic_string_span<value_type, Extent>;
 
-    size_type length() const { return sv_.length(); }
+    constexpr basic_zstring_span(impl_type span) noexcept
+        : sp_(span)
+    {
+        // expects a zero-terminated span
+        Expects(span[span.size() - 1] == '\0');
+    }
 
-    pointer assume0() const { return data(); }
-    string_span_type ensure_z() const { return gsl::ensure_z(sv_); }
+    constexpr bool empty() const noexcept { return sp_.size() == 0; }
 
-    iterator begin() const { return sv_.begin(); }
-    iterator end() const { return sv_.end(); }
+    constexpr string_span_type as_string_span() const noexcept { return sp_.first(sp_.size()-1); }
+
+    constexpr string_span_type ensure_z() const noexcept { return gsl::ensure_z(sp_); }
+
+    constexpr const_zstring_type assume_z() const noexcept { return sp_.data(); }
 
 private:
-    impl_type sv_;
+    impl_type sp_;
 };
 
 template <size_t Max = dynamic_range>
-using zstring_builder = basic_zstring_builder<char, Max>;
+using zstring_span = basic_zstring_span<char, Max>;
 
 template <size_t Max = dynamic_range>
-using wzstring_builder = basic_zstring_builder<wchar_t, Max>;
-}
+using wzstring_span = basic_zstring_span<wchar_t, Max>;
+
+template <size_t Max = dynamic_range>
+using czstring_span = basic_zstring_span<const char, Max>;
+
+template <size_t Max = dynamic_range>
+using cwzstring_span = basic_zstring_span<const wchar_t, Max>;
+
+} // namespace GSL
 
 // operator ==
 template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,

tests/string_span_tests.cpp

@@ -830,6 +830,120 @@ SUITE(string_span_tests)
         CHECK(wspan.length() == 5);
 #endif
     }
+
+    czstring_span<> CreateTempName(string_span<> span)
+    {
+        Expects(span.size() > 1);
+
+        int last = 0;
+        if (span.size() > 4)
+        {
+            span[0] = 't';
+            span[1] = 'm';
+            span[2] = 'p';
+            last = 3;
+        }
+        span[last] = '\0';
+
+        auto ret = span.subspan(0, 4);
+        return ret;
+    }
+
+    TEST(zstring)
+    {
+
+        // create zspan from zero terminated string
+        {
+            char buf[1];
+            buf[0] = '\0';
+
+            zstring_span<> zspan({ buf, 1 });
+
+            CHECK(strlen(zspan.assume_z()) == 0);
+            CHECK(zspan.as_string_span().size() == 0);
+            CHECK(zspan.ensure_z().size() == 0);
+        }
+
+        // create zspan from non-zero terminated string
+        {
+            char buf[1];
+            buf[0] = 'a';
+
+            auto workaround_macro = [&]() { zstring_span<> zspan({ buf, 1 }); };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+
+        // usage scenario: create zero-terminated temp file name and pass to a legacy API
+        {
+            char buf[10];
+
+            auto name = CreateTempName({ buf, 10 });
+            if (!name.empty())
+            {
+                czstring<> str = name.assume_z();
+                CHECK(strlen(str) == 3);
+                CHECK(*(str+3) == '\0');
+            }
+        }
+
+    }
+
+    cwzstring_span<> CreateTempNameW(wstring_span<> span)
+    {
+        Expects(span.size() > 1);
+
+        int last = 0;
+        if (span.size() > 4)
+        {
+            span[0] = L't';
+            span[1] = L'm';
+            span[2] = L'p';
+            last = 3;
+        }
+        span[last] = L'\0';
+
+        auto ret = span.subspan(0, 4);
+        return ret;
+    }
+
+    TEST(wzstring)
+    {
+
+        // create zspan from zero terminated string
+        {
+            wchar_t buf[1];
+            buf[0] = L'\0';
+
+            wzstring_span<> zspan({ buf, 1 });
+
+            CHECK(wcsnlen(zspan.assume_z(), 1) == 0);
+            CHECK(zspan.as_string_span().size() == 0);
+            CHECK(zspan.ensure_z().size() == 0);
+        }
+
+        // create zspan from non-zero terminated string
+        {
+            wchar_t buf[1];
+            buf[0] = L'a';
+
+            auto workaround_macro = [&]() { wzstring_span<> zspan({ buf, 1 }); };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+
+        // usage scenario: create zero-terminated temp file name and pass to a legacy API
+        {
+            wchar_t buf[10];
+
+            auto name = CreateTempNameW({ buf, 10 });
+            if (!name.empty())
+            {
+                cwzstring<> str = name.assume_z();
+                CHECK(wcsnlen(str, 10) == 3);
+                CHECK(*(str + 3) == L'\0');
+            }
+        }
+
+    }
 }
 
 int main(int, const char *[])