- •Thinking in C++ 2nd edition Volume 2: Standard Libraries & Advanced Topics
- •Preface
- •What’s new in the second edition
- •What’s in Volume 2 of this book
- •How to get Volume 2
- •Prerequisites
- •Learning C++
- •Goals
- •Chapters
- •Exercises
- •Exercise solutions
- •Source code
- •Language standards
- •Language support
- •The book’s CD ROM
- •Seminars, CD Roms & consulting
- •Errors
- •Acknowledgements
- •Library overview
- •1: Strings
- •What’s in a string
- •Creating and initializing C++ strings
- •Initialization limitations
- •Operating on strings
- •Appending, inserting and concatenating strings
- •Replacing string characters
- •Concatenation using non-member overloaded operators
- •Searching in strings
- •Finding in reverse
- •Finding first/last of a set
- •Removing characters from strings
- •Stripping HTML tags
- •Comparing strings
- •Using iterators
- •Iterating in reverse
- •Strings and character traits
- •A string application
- •Summary
- •Exercises
- •2: Iostreams
- •Why iostreams?
- •True wrapping
- •Iostreams to the rescue
- •Sneak preview of operator overloading
- •Inserters and extractors
- •Manipulators
- •Common usage
- •Line-oriented input
- •Overloaded versions of get( )
- •Reading raw bytes
- •Error handling
- •File iostreams
- •Open modes
- •Iostream buffering
- •Seeking in iostreams
- •Creating read/write files
- •User-allocated storage
- •Output strstreams
- •Automatic storage allocation
- •Proving movement
- •A better way
- •Output stream formatting
- •Internal formatting data
- •Format fields
- •Width, fill and precision
- •An exhaustive example
- •Formatting manipulators
- •Manipulators with arguments
- •Creating manipulators
- •Effectors
- •Iostream examples
- •Code generation
- •Maintaining class library source
- •Detecting compiler errors
- •A simple datalogger
- •Generating test data
- •Verifying & viewing the data
- •Counting editor
- •Breaking up big files
- •Summary
- •Exercises
- •3: Templates in depth
- •Nontype template arguments
- •Typedefing a typename
- •Using typename instead of class
- •Function templates
- •A string conversion system
- •A memory allocation system
- •Type induction in function templates
- •Taking the address of a generated function template
- •Local classes in templates
- •Applying a function to an STL sequence
- •Template-templates
- •Member function templates
- •Why virtual member template functions are disallowed
- •Nested template classes
- •Template specializations
- •A practical example
- •Pointer specialization
- •Partial ordering of function templates
- •Design & efficiency
- •Preventing template bloat
- •Explicit instantiation
- •Explicit specification of template functions
- •Controlling template instantiation
- •Template programming idioms
- •Summary
- •Containers and iterators
- •STL reference documentation
- •The Standard Template Library
- •The basic concepts
- •Containers of strings
- •Inheriting from STL containers
- •A plethora of iterators
- •Iterators in reversible containers
- •Iterator categories
- •Input: read-only, one pass
- •Output: write-only, one pass
- •Forward: multiple read/write
- •Bidirectional: operator--
- •Random-access: like a pointer
- •Is this really important?
- •Predefined iterators
- •IO stream iterators
- •Manipulating raw storage
- •Basic sequences: vector, list & deque
- •Basic sequence operations
- •vector
- •Cost of overflowing allocated storage
- •Inserting and erasing elements
- •deque
- •Converting between sequences
- •Cost of overflowing allocated storage
- •Checked random-access
- •list
- •Special list operations
- •list vs. set
- •Swapping all basic sequences
- •Robustness of lists
- •Performance comparison
- •A completely reusable tokenizer
- •stack
- •queue
- •Priority queues
- •Holding bits
- •bitset<n>
- •vector<bool>
- •Associative containers
- •Generators and fillers for associative containers
- •The magic of maps
- •A command-line argument tool
- •Multimaps and duplicate keys
- •Multisets
- •Combining STL containers
- •Creating your own containers
- •Summary
- •Exercises
- •5: STL Algorithms
- •Function objects
- •Classification of function objects
- •Automatic creation of function objects
- •Binders
- •Function pointer adapters
- •SGI extensions
- •A catalog of STL algorithms
- •Support tools for example creation
- •Filling & generating
- •Example
- •Counting
- •Example
- •Manipulating sequences
- •Example
- •Searching & replacing
- •Example
- •Comparing ranges
- •Example
- •Removing elements
- •Example
- •Sorting and operations on sorted ranges
- •Sorting
- •Example
- •Locating elements in sorted ranges
- •Example
- •Merging sorted ranges
- •Example
- •Set operations on sorted ranges
- •Example
- •Heap operations
- •Applying an operation to each element in a range
- •Examples
- •Numeric algorithms
- •Example
- •General utilities
- •Creating your own STL-style algorithms
- •Summary
- •Exercises
- •Perspective
- •Duplicate subobjects
- •Ambiguous upcasting
- •virtual base classes
- •The "most derived" class and virtual base initialization
- •"Tying off" virtual bases with a default constructor
- •Overhead
- •Upcasting
- •Persistence
- •MI-based persistence
- •Improved persistence
- •Avoiding MI
- •Mixin types
- •Repairing an interface
- •Summary
- •Exercises
- •7: Exception handling
- •Error handling in C
- •Throwing an exception
- •Catching an exception
- •The try block
- •Exception handlers
- •Termination vs. resumption
- •The exception specification
- •Better exception specifications?
- •Catching any exception
- •Rethrowing an exception
- •Uncaught exceptions
- •Function-level try blocks
- •Cleaning up
- •Constructors
- •Making everything an object
- •Exception matching
- •Standard exceptions
- •Programming with exceptions
- •When to avoid exceptions
- •Not for asynchronous events
- •Not for ordinary error conditions
- •Not for flow-of-control
- •You’re not forced to use exceptions
- •New exceptions, old code
- •Typical uses of exceptions
- •Always use exception specifications
- •Start with standard exceptions
- •Nest your own exceptions
- •Use exception hierarchies
- •Multiple inheritance
- •Catch by reference, not by value
- •Throw exceptions in constructors
- •Don’t cause exceptions in destructors
- •Avoid naked pointers
- •Overhead
- •Summary
- •Exercises
- •8: Run-time type identification
- •The “Shape” example
- •What is RTTI?
- •Two syntaxes for RTTI
- •Syntax specifics
- •Producing the proper type name
- •Nonpolymorphic types
- •Casting to intermediate levels
- •void pointers
- •Using RTTI with templates
- •References
- •Exceptions
- •Multiple inheritance
- •Sensible uses for RTTI
- •Revisiting the trash recycler
- •Mechanism & overhead of RTTI
- •Creating your own RTTI
- •Explicit cast syntax
- •Summary
- •Exercises
- •9: Building stable systems
- •Shared objects & reference counting
- •Reference-counted class hierarchies
- •Finding memory leaks
- •An extended canonical form
- •Exercises
- •10: Design patterns
- •The pattern concept
- •The singleton
- •Variations on singleton
- •Classifying patterns
- •Features, idioms, patterns
- •Basic complexity hiding
- •Factories: encapsulating object creation
- •Polymorphic factories
- •Abstract factories
- •Virtual constructors
- •Destructor operation
- •Callbacks
- •Observer
- •The “interface” idiom
- •The “inner class” idiom
- •The observer example
- •Multiple dispatching
- •Visitor, a type of multiple dispatching
- •Efficiency
- •Flyweight
- •The composite
- •Evolving a design: the trash recycler
- •Improving the design
- •“Make more objects”
- •A pattern for prototyping creation
- •Trash subclasses
- •Parsing Trash from an external file
- •Recycling with prototyping
- •Abstracting usage
- •Applying double dispatching
- •Implementing the double dispatch
- •Applying the visitor pattern
- •More coupling?
- •RTTI considered harmful?
- •Summary
- •Exercises
- •11: Tools & topics
- •The code extractor
- •Debugging
- •Trace macros
- •Trace file
- •Abstract base class for debugging
- •Tracking new/delete & malloc/free
- •CGI programming in C++
- •Encoding data for CGI
- •The CGI parser
- •Testing the CGI parser
- •Using POST
- •Handling mailing lists
- •Maintaining your list
- •Mailing to your list
- •A general information-extraction CGI program
- •Parsing the data files
- •Summary
- •Exercises
- •General C++
- •My own list of books
- •Depth & dark corners
- •Design Patterns
- •Index
2: Iostreams
There’s much more you can do with the general I/O problem than just take standard I/O and turn it into a class.
Wouldn’t it be nice if you could make all the usual “receptacles” – standard I/O, files and even blocks of memory – look the same, so you need to remember only one interface? That’s the idea behind iostreams. They’re much easier, safer, and often more efficient than the assorted functions from the Standard C stdio library.
Iostream is usually the first class library that new C++ programmers learn to use. This chapter explores the use of iostreams, so they can replace the C I/O functions through the rest of the book. In future chapters, you’ll see how to set up your own classes so they’re compatible with iostreams.
Why iostreams?
You may wonder what’s wrong with the good old C library. And why not “wrap” the C library in a class and be done with it? Indeed, there are situations when this is the perfect thing to do, when you want to make a C library a bit safer and easier to use. For example, suppose you want to make sure a stdio file is always safely opened and properly closed, without relying on the user to remember to call the close( ) function:
//: C02:FileClass.h
// Stdio files wrapped #ifndef FILECLAS_H #define FILECLAS_H #include <cstdio>
class FileClass { std::FILE* f;
public:
FileClass(const char* fname, const char* mode="r"); ~FileClass();
std::FILE* fp();
};
#endif // FILECLAS_H ///:~
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In C when you perform file I/O, you work with a naked pointer to a FILE struct, but this class wraps around the pointer and guarantees it is properly initialized and cleaned up using the constructor and destructor. The second constructor argument is the file mode, which defaults to “r” for “read.”
To fetch the value of the pointer to use in the file I/O functions, you use the fp( ) access function. Here are the member function definitions:
//: C02:FileClass.cpp {O} // Implementation #include "FileClass.h" #include <cstdlib>
using namespace std;
FileClass::FileClass(const char* fname, const char* mode){ f = fopen(fname, mode);
if(f == NULL) {
printf("%s: file not found\n", fname); exit(1);
}
}
FileClass::~FileClass() { fclose(f); }
FILE* FileClass::fp() { return f; } ///:~
The constructor calls fopen( ),as you would normally do, but it also checks to ensure the result isn’t zero, which indicates a failure upon opening the file. If there’s a failure, the name of the file is printed and exit( ) is called.
The destructor closes the file, and the access function fp( )returns f. Here’s a simple example using class FileClass:
//: C02:FileClassTest.cpp //{L} FileClass
// Testing class File #include "FileClass.h" #include "../require.h" using namespace std;
int main(int argc, char* argv[]) { requireArgs(argc, 1);
FileClass f(argv[1]); // Opens and tests const int bsize = 100;
char buf[bsize]; while(fgets(buf, bsize, f.fp()))
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puts(buf);
} // File automatically closed by destructor
///:~
You create the FileClass object and use it in normal C file I/O function calls by calling fp( ). When you’re done with it, just forget about it, and the file is closed by the destructor at the end of the scope.
True wrapping
Even though the FILE pointer is private, it isn’t particularly safe because fp( ) retrieves it. The only effect seems to be guaranteed initialization and cleanup, so why not make it public, or use a struct instead? Notice that while you can get a copy of f using fp( ), you cannot assign to f – that’s completely under the control of the class. Of course, after capturing the pointer returned by fp( ), the client programmer can still assign to the structure elements, so the safety is in guaranteeing a valid FILE pointer rather than proper contents of the structure.
If you want complete safety, you have to prevent the user from direct access to the FILE pointer. This means some version of all the normal file I/O functions will have to show up as class members, so everything you can do with the C approach is available in the C++ class:
//: C02:Fullwrap.h
// Completely hidden file IO #ifndef FULLWRAP_H
#define FULLWRAP_H
class File { std::FILE* f;
std::FILE* F(); // Produces checked pointer to f public:
File(); // Create object but don't open file File(const char* path,
const char* mode = "r"); ~File();
int open(const char* path,
const char* mode = "r"); int reopen(const char* path,
const char* mode);
int getc();
int ungetc(int c); int putc(int c);
int puts(const char* s); char* gets(char* s, int n);
int printf(const char* format, ...); size_t read(void* ptr, size_t size,
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size_t n);
size_t write(const void* ptr,
size_t size, size_t n);
int eof(); int close(); int flush();
int seek(long offset, int whence); int getpos(fpos_t* pos);
int setpos(const fpos_t* pos); long tell();
void rewind();
void setbuf(char* buf);
int setvbuf(char* buf, int type, size_t sz); int error();
void clearErr();
};
#endif // FULLWRAP_H ///:~
This class contains almost all the file I/O functions from cstdio. vfprintf( ) is missing; it is used to implement the printf( ) member function.
File has the same constructor as in the previous example, and it also has a default constructor. The default constructor is important if you want to create an array of File objects or use a File object as a member of another class where the initialization doesn’t happen in the constructor (but sometime after the enclosing object is created).
The default constructor sets the private FILE pointer f to zero. But now, before any reference to f, its value must be checked to ensure it isn’t zero. This is accomplished with the last member function in the class, F( ), which is private because it is intended to be used only by other member functions. (We don’t want to give the user direct access to the FILE structure in this class.)6
This is not a terrible solution by any means. It’s quite functional, and you could imagine making similar classes for standard (console) I/O and for in-core formatting (reading/writing a piece of memory rather than a file or the console).
The big stumbling block is the runtime interpreter used for the variable-argument list functions. This is the code that parses through your format string at runtime and grabs and interprets arguments from the variable argument list. It’s a problem for four reasons.
1.Even if you use only a fraction of the functionality of the interpreter, the whole thing gets loaded. So if you say:
6 The implementation and test files for FULLWRAP are available in the freely distributed source code for this book. See preface for details.
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