Creating and Using Streams Instantiated on User-Defined Types

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Apache C++ Standard Library User's Guide

41.3 Creating and Using Streams Instantiated on User-Defined Types

Once all the support work is finished, you can instantiate a stream class template on your type and begin to use it--well, not quite. Because the new stream requires the new facets you've defined, you must first create a new locale containing these facets and then imbue that locale on your stream. You can do this as follows:

typedef std::basic_fstream<Echar,Etraits> Estream; // 1
std::locale Eloc(std::locale(std::locale(),
 new Ecodecvt),new Ectype); // 2
Estream foo("foo.txt"); // 3
foo.imbue(Eloc); // 4

//1 Typedef the special stream type to something convenient.

//2 Construct a new locale object and replace the std::codecvt and std::ctype facets with the ones we've defined for Echar. We use the constructor that takes an existing locale and a new facet to construct a locale with a new codecvt facet, and then use it again to get a locale with both new facets.

//3 Construct an Estream.

//4 Imbue the new locale object containing our replacement facets onto the Estream.

Now we're ready to insert Echars into the stream and read them back in:

Echar e[10];
Estream::pos_type pos = foo.tellp(); //1
foo << 10; //2
foo.seekg(pos); //3
foo >> e; //4

//1 Get current position.

//2 Write out the integer 10.

//3 Seek back.

//4 Read in the string 10 as Echars.

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