vb.net 2008 barcode generator System::String and Other I/O Systems in Visual C#.NET

Generator PDF 417 in Visual C#.NET System::String and Other I/O Systems

Still prefer the trusty C runtime function printf Unless you re compiling with safe mode (the /clr:safe compiler option), you can still use the C Runtime (CRT) Library or the iostream library if that s what you prefer, although the resulting code will not be verifiably safe from memory corruption problems. Most CRT functions taking a variable argument list will work with System::String, as in Listing 5-16. Note that as of Visual C++ 2005, it is recommended that

you use the more secure variants of the standard CRT functions. While these are not yet part of the ANSI standard, they have been proposed as extensions to the standard. Listing 5-16. Using printf // cli_printf.cpp using namespace System; #include <stdio.h> int main() { String^ str = "managed string"; // The string is automatically converted to a // char array for printf_s. printf_s("%s", str ); } The output of Listing 5-16 is shown here:

The conversion for printf_s (and printf) is due to the String class s ability to be converted via a variable argument list and not a general conversion to const char *. For example, the following line: printf_s(str); produces an error: cli_printf.cpp(12) : error C2664: 'printf_s' : cannot convert parameter 1 from ' System::String ^' to 'const char *' No user-defined-conversion operator available, or Cannot convert a managed type to an unmanaged type Using cout with System::String is a bit more complicated. The string must be marshaled as a native data type that the overloaded shift operator (<<) supports, and because we are getting a native pointer to managed data (which could be moved by the garbage collector) it must be artificially fixed in memory during the time that the native data type is active. We accomplish this by declaring a pinning pointer (pin_ptr), as shown in Listing 5-17. The first step is to use PtrToStringChars (defined in vcclr.h) to get a pointer into the underlying wide character array that represents the string, and assign that to a pinning pointer that fixes the data it points to as long as the pinning pointer is in scope. This pinning pointer must in turn be converted to a type that the shift operator supports, so we use static_cast to convert it to const wchar_t* and pass that to the expression involving wcout, the wide character version of cout.

Listing 5-17. Using a Pinning Pointer // string_wcout.cpp #include <vcclr.h> #include <iostream> using namespace std; using namespace System; int main() { String^ s = "Testing String conversion to iostream."; pin_ptr<const wchar_t> ptr = PtrToStringChars(s); wcout << static_cast<const wchar_t*>( ptr ) << endl; } The output of Listing 5-17 is as follows:

Listing 5-17 is just a taste of the concerns you have to deal with in mixing native and managed libraries. Using CLR types with classic C++ libraries is an example of C++ interop, which is discussed in greater detail in 12. The preceding sections looked in detail at the String type, including its methods, support for the + operator, and the Format method in detail, including specific formatting rules for numeric output. You also saw the StringBuilder class for manipulating strings in-place, and the Console class for input and output to the console or command-line window, including a discussion of the In, Out, and Error representations of stdin, stdout, and stderr. I covered the Write and WriteLine methods, the Read and Readline methods, and file I/O using the StreamWriter and StreamReader classes, and corresponding functionality for string I/O in the StringWriter and StringReader classes. Now let s look at another fundamental type: the array.

The C++/CLI managed array provides the functionality of a classic array and is also an object type complete with methods. The methods simplify common tasks such as getting the length of the array, sorting, and handling thread synchronization. A managed array is declared as follows: array< type, rank >^ array_name; This is read as array_name is a handle to a managed array of some type and number of dimensions (rank). Here are some examples of declarations of managed arrays: