字符串（C++/CLI 和 C++/CX）
Windows 运行时和公共语言运行时将字符串表示为，已分配内存受自动管理的对象。 也就是说，当字符串变量超出范围或应用程序结束时，不必显式放弃字符串的内存。 若要指明字符串对象的生存期受自动管理，请使用指向对象的句柄 (^) 修饰符来声明字符串类型。
Windows 运行时
Windows 运行时体系结构要求，String 数据类型必须位于 Platform 命名空间中。 为了方便起见，Visual C++ 还在 default 命名空间中提供了 string 数据类型（它是 Platform::String 的同义词）。
语法
// compile with /ZW
using namespace Platform;
using namespace default;
Platform::String^ MyString1 = "The quick brown fox";
String^ MyString2 = "jumped over the lazy dog.";
String^ MyString3 = "Hello, world!";
要求
编译器选项：/ZW
公共语言运行时
当你使用 /clr 进行编译时，编译器会将字符串文字转换为 String 类型的字符串。 为了保持与现有代码的向后兼容性，有两个例外情况：
编译器还内置了对三个运算符的支持，可以通过重写它们来自定义行为：
System::String^ 运算符 +( System::String, System::String)；
System::String^ 运算符 +( System::Object, System::String)；
System::String^ 运算符 +( System::String, System::Object)；
如果传递的是 String，编译器会根据需要进行装箱，然后将对象（包含 ToString）与字符串连接起来。
注意
脱字号（“^”）指明，声明的变量是指向 C++/CLI 托管对象的句柄。
有关详细信息，请参阅字符串文字和字符文字。
要求
编译器选项： /clr
示例
下面的代码示例展示了如何连接和比较字符串。
// string_operators.cpp
// compile with: /clr
// In the following code, the caret ("^") indicates that the
// declared variable is a handle to a C++/CLI managed object.
using namespace System;
int main() {
String^ a = gcnew String("abc");
String^ b = "def"; // same as gcnew form
Object^ c = gcnew String("ghi");
char d[100] = "abc";
// variables of System::String returning a System::String
Console::WriteLine(a + b);
Console::WriteLine(a + c);
Console::WriteLine(c + a);
// accessing a character in the string
Console::WriteLine(a[2]);
// concatenation of three System::Strings
Console::WriteLine(a + b + c);
// concatenation of a System::String and string literal
Console::WriteLine(a + "zzz");
// you can append to a System::String^
Console::WriteLine(a + 1);
Console::WriteLine(a + 'a');
Console::WriteLine(a + 3.1);
// test System::String^ for equality
a += b;
Console::WriteLine(a);
a = b;
if (a == b)
Console::WriteLine("a and b are equal");
a = "abc";
if (a != b)
Console::WriteLine("a and b are not equal");
// System:String^ and tracking reference
String^% rstr1 = a;
Console::WriteLine(rstr1);
// testing an empty System::String^
String^ n;
if (n == nullptr)
Console::WriteLine("n is empty");
}
abcdef
abcghi
ghiabc
c
abcdefghi
abczzz
abc1
abc97
abc3.1
abcdef
a and b are equal
a and b are not equal
abc
n is empty
下面的示例展示了可以重载编译器提供的运算符，编译器会根据 String 类型查找函数重载。
// string_operators_2.cpp
// compile with: /clr
using namespace System;
// a string^ overload will be favored when calling with a String
void Test_Overload(const char * a) {
Console::WriteLine("const char * a");
}
void Test_Overload(String^ a) {
Console::WriteLine("String^ a");
}
// overload will be called instead of compiler defined operator
String^ operator +(String^ a, String^ b) {
return ("overloaded +(String^ a, String^ b)");
}
// overload will be called instead of compiler defined operator
String^ operator +(Object^ a, String^ b) {
return ("overloaded +(Object^ a, String^ b)");
}
// overload will be called instead of compiler defined operator
String^ operator +(String^ a, Object^ b) {
return ("overloaded +(String^ a, Object^ b)");
}
int main() {
String^ a = gcnew String("abc");
String^ b = "def"; // same as gcnew form
Object^ c = gcnew String("ghi");
char d[100] = "abc";
Console::WriteLine(a + b);
Console::WriteLine(a + c);
Console::WriteLine(c + a);
Test_Overload("hello");
Test_Overload(d);
}
overloaded +(String^ a, String^ b)
overloaded +(String^ a, Object^ b)
overloaded +(Object^ a, String^ b)
String^ a
const char * a
下面的示例展示了编译器区分本机字符串和 String 字符串。
// string_operators_3.cpp
// compile with: /clr
using namespace System;
int func() {
throw "simple string"; // const char *
};
int func2() {
throw "string" + "string"; // returns System::String
};
template<typename T>
void func3(T t) {
Console::WriteLine(T::typeid);
}
int main() {
try {
func();
}
catch(char * e) {
Console::WriteLine("char *");
}
try {
func2();
}
catch(String^ str) {
Console::WriteLine("String^ str");
}
func3("string"); // const char *
func3("string" + "string"); // returns System::String
}
char *
String^ str
System.SByte*
System.String