Add string substring operation

include/rexy/string_base.hpp

@@ -295,6 +295,10 @@ namespace rexy{
 		void append(const_pointer data)
 			noexcept(noexcept(this->allocate(0)) &&
 			         noexcept(this->deallocate(nullptr,0)));
+
+		template<class Alloc = allocator_type>
+		basic_string<value_type,Alloc> substring(size_type start, size_type end)const;
+
 		pointer release(void)noexcept(noexcept(this->allocate(0)));
 		using detail::hasallocator<Allocator>::allocator;
 	};

include/rexy/string_base.tpp

@@ -211,6 +211,16 @@ namespace rexy{
 			append(data, cx::strlen(data));
 	}
 
+	template<class Char, class Allocator>
+	template<class Alloc>
+	auto basic_string<Char,Allocator>::substring(size_type start, size_type end)const -> basic_string<value_type,Alloc>{
+		if(start > end || end > this->length())
+			return {};
+		const size_type newlen = end - start;
+		basic_string<value_type,Alloc> tmp(newlen);
+		tmp.append(this->get() + start, newlen);
+		return tmp;
+	}
 	template<class Char, class Allocator>
 	auto basic_string<Char,Allocator>::release(void)noexcept(noexcept(this->allocate(0))) -> pointer{
 		if(this->islong()){

tests/basic_string.cpp

@@ -235,7 +235,13 @@ void check_long_append(){
 	test_str str1(startdata1);
 	str1.append("stuff");
 	if(strcmp(str1.get(), appendeddata))
-		error("long append should have resulted in this is another really long string that should ensure that it makes some sort of dyn alloc for big bufstuff");
+		error("long append should have resulted in this is another really long string that should ensure that it makes some sort of dyn alloc for big bufstuff\n");
+}
+void check_substring(){
+	rexy::string test = "this is a test string";
+	rexy::string test2 = test.substring(5, 7);
+	if(strcmp(test2.get(), "is") || test2.length() != 2)
+		error("substring operation should have resulted in 'is'\n");
 }
 
 int main(){
@@ -246,4 +252,5 @@ int main(){
 	check_long_assignment();
 	check_short_append();
 	check_long_append();
+	check_substring();
 }