The Mutex package provides a way to synchronize access to user-defined objects. It consists of a single class, Mutex, that manages the creation, locking and unlocking of Mutex objects.

Construction of a Mutex object creates a recursive mutex that users can lock and unlock using the appropriate member functions or parameterized manipulators. A recursive mutex is a mutex that can be locked many times by the same thread without causing the thread to enter a deadlock state. To completely unlock this kind of mutex, the thread must unlock the mutex the same number of times that the thread locked the mutex. For more information see the Guide to DECthreads manual.

Provides a means whereby users can synchronize access to user-defined objects.

Header File

#include <mutex.hxx>

Alternative Header

#include <mutex.h>

Declaration

class Mutex { public: Mutex(); ~Mutex(); void lock(); void unlock(); int trylock(); };

Description

The synchronization process consists of locking and unlocking Mutex objects associated with user-defined objects. Digital recommends that users create a Mutex object for each user-defined object that needs to be synchronized between threads. Users are then responsible for locking and unlocking the Mutex object to coordinate access to the associated object.

To do the locking and unlocking, you can use the lock and unlock member functions (see Example). Alternatively, if a user-defined object is derived from the istream or ostream classes, you can use the lock and unlock parameterized manipulators, where the parameter is the Mutex object (see the Global Declarations section in Chapter 4).

Constructors and Destructors

Mutex()

Constructs a Mutex object, in effect creating but not locking a recursive mutex.

~Mutex()

Deletes a Mutex object.

Member Functions

void lock()

Locks a recursive mutex. If the mutex is locked by another thread, the current thread is blocked until the mutex becomes available.

void unlock()

Unlocks a recursive mutex.

int trylock()

Immediately returns to the caller a value of 0 if the mutex is already locked by another thread. Otherwise, this function locks the mutex and returns a value of 1.

Example

#include <string.hxx> 
#include <mutex.hxx> 
   .
   .
   .
String string1; 
Mutex string1_lock; 
 
string1_lock.lock(); 
string1 = "Hello, "; 
string1 += "how are you?"; 
cout << string1; 
string1_lock.unlock(); 
      

This example synchronizes a sequence of operations on a String object, using the lock() and unlock() member functions.

The Objection package provides a way to implement simple error handling in DEC C++. You can use this package to catch run-time errors encountered in using classes, and to change or restore actions associated with such errors.

This typedef is used by, but is not a member of, the Objection class.

Header

#include <objection.hxx>

Alternative Header

#include <Objection.h>

Declaration

typedef int Objection_action(const char*);

Type

Objection_action

Is the type of an action routine that can be called by the function Objection::raise.

Provides the capability to handle and report errors.

Header

#include <objection.hxx>

Alternative Header

#include <Objection.h>

Declaration

class Objection { public: Objection(); Objection(Objection_action *); int raise(const char * = ""); Objection_action *appoint(Objection_action *); Objection_action *appoint(); Objection_action *ignore(); };

Description

This class provides ways to handle objections. An objection is a potential error condition that your program can encounter. The user appoints an error-handling function. An Objection object's raise() function invokes the appointed function by passing it a character string that contains an error message. At any point in your program, you can appoint a new error-handling function, reappoint the original function, or specify that an objection be ignored.

Constructors

Objection()

Constructs an Objection object with no default action (error handler).

Objection(Objection_action *new_action)

Constructs an Objection object with a pointer to the default error handler. The handler is a function that takes one parameter of type const char *msg and returns an int. See the raise() member function for more information.

Member Functions

Objection_action *appoint()

Specifies that the handler for the objection is the default error handler (if one exists) and returns the previous action associated with the specified objection. Specifies that the objection not be ignored.

Objection_action *appoint(Objection_action *new_action)

Specifies a new handler for the objection and returns the previous action associated with the specified objection. Specifies that the objection not be ignored.

Objection_action *ignore()

Specifies that the objection be ignored (no error handler is invoked if the objection is raised). This function returns the previous action associated with the specified objection.

int raise(const char *msg = "")

Raises a specified objection, passing a string (error message) to an error handler (if one exists). If no handler exists, or if the handler returns a 0, the default handler is called. The raise function returns the value returned by the last handler it called.

If no default handler exists, then the function returns 0. A 0 is also returned if the objection is ignored. Generally, the return of a nonzero value means that the error handling succeeded, and the return of a 0 value means the error handling failed.

The following example changes the default error handler for the
stack(int)::overflow_error objection:

#include <stdlib.h> #include <vector.hxx> #include <objection.hxx> vectordeclare(int) stackdeclare(int) vectorimplement(int) stackimplement(int) stack(int) s(10); int error(const char *errmsg) { cerr << "ERROR TRAPPED: " << errmsg << " -- ABORTING\n"; cerr.flush(); abort(); return 0; } void main() { Objection_action *save_action; save_action = stack(int)::overflow_error.appoint(error); for(int i=0; i<100; i++) //push too many things onto stack s.push(i); stack(int)::overflow_error.appoint(save_action); }

When this example executes, the following message prints out:

ERROR TRAPPED: Stack underflow -- ABORTING IOT trap (core dumped)

The Stopwatch package provides ways to measure intervals of program execution time. The package consists of a single class, Stopwatch. Typically, you use this class during the performance-tuning phase of program development.

Provides the means to measure intervals of time between specified program events.

Header

#include <stopwatch.hxx>

Alternative Header

#include <Stopwatch.h>

Declaration

class Stopwatch { public: Stopwatch(); void start(); void stop(); void reset(); int status() const; double system() const; double user() const; double real() const; static double resolution(); };

Description

Objects of this class measure program execution time and return the result in floating-point seconds. The class includes the start, stop, and reset functions familiar to users of a mechanical stopwatch.

You can time the entire program or select certain portions of the program to time; for example, a specified loop or program module. You can create a different Stopwatch object for each independent program activity, and name each according to the activity you intend to measure.

Constructor

Stopwatch()

Constructs a Stopwatch object with both time and running status initialized to 0.

Member Functions

double real() const

Returns real time (clock time) in double-precision, floating-point seconds. You can call this function while the stopwatch is running.

void reset()

Resets the current time measurement to 0 without affecting the value of status(). If status() is initially nonzero, time measurement continues uninterrupted after resetting.

double resolution()

Returns the (system dependent) resolution of measured time in double-precision, floating-point seconds.

void start()

Begins measuring program execution time when status() is initially 0 (status() becomes nonzero as a consequence of the call). If status()is initially nonzero, the call has no effect.

int status() const

Indicates whether the stopwatch is running (returns a value of 1) or not running (returns a value of 0).

void stop()

Halts measurement of program execution time when status() is initially nonzero (status() becomes 0 as a consequence of the call). If status()is initially 0, the call has no effect.

double system() const

Returns the system CPU time in double-precision, floating-point seconds. You can call this function while the stopwatch is running.

double user() const

Returns the user CPU time in double-precision, floating-point seconds. You can call this function while the stopwatch is running.

System Environment

A typical value for the resolution of execution time is 1/60 second.

Example

Stopwatch w ; 
w.start() ; 
//...
// some computation you want to time goes here 
//...
w.stop() ; 
cout << "elapsed time was " << w.user() << "\n"; 
      

Displays the number of seconds the computation takes to run. The result is a double-precision value.

The String package consists of the single class String. This class provides ways to assign, concatenate, and compare character strings. This class also provides methods for substring creation and for vector access to a character string.

Provides the capabilities for manipulating sequences of characters.

Header

#include <string.hxx>

Alternative Header

#include <String.h>

Declaration

class String { friend ostream &operator<<(ostream &, const String &); friend istream &operator>>(istream &, String &); friend int operator==(const String &, const String &); friend int operator==(const String &, const char *); friend int operator==(const char *, const String &); friend int operator!=(const String &, const String &); friend int operator!=(const String &, const char *); friend int operator!=(const char *, const String &); friend int operator<(const String &, const String &); friend int operator<(const String &, const char *); friend int operator<(const char *, const String &); friend int operator>(const String &, const String &); friend int operator>(const String &, const char *); friend int operator>(const char *, const String &); friend int operator<=(const String &, const String &); friend int operator<=(const String &, const char *); friend int operator<=(const char *, const String &); friend int operator>=(const String &, const String &); friend int operator>=(const String &, const char *); friend int operator>=(const char *, const String &); friend String operator+(const String &, const String &); friend String operator+(const String &, const char *); friend String operator+(const char *, const String &); public: String(); String(const String &); String(const char *); String(const char &); ~String(); String &operator=(const String &); String &operator=(const char *); operator char * () const; operator const char * () const; String &operator+=(const String &); String &operator+=(const char *); String operator()(int, int) const; unsigned int length() const; String upper() const; String lower() const; int match(const String &) const; int index(const String &) const; char operator[](int) const; char &operator[](int); };

Description

This class provides the means for manipulating sequences of characters, each of which is of the type char. For some applications, the services provided are like those provided by the traditional C string library (strcpy, strcmp, and so forth), but are more efficient and convenient in the context of C++. Overloaded operators provide ways to assign, concatenate, and compare strings. New operators provide simple notations for substring creation and vector access into the string.

All comparisons are lexicographic, with the ordering dependent on the character set in which the string is encoded.

An index value of 0 indicates the first character in a string object.

Constructors and Destructors

String()

Constructs a String object initialized to an empty string.

String(const char *s)

Constructs a String object and initializes it to the null-terminated sequence of characters.

String(const char &c)

Constructs a String object with a reference to a char datum to initialize the string.

String(const String &x)

Constructs a String object with a reference to another String to initialize the first String.

~String()

Deletes a String object; no user action is required.

Overloaded Operators

String operator + (const char *s, const String &x)

Concatenates a null-terminated sequence of characters to a String object.

String operator + (const String &x, const char *s)

Concatenates a String object with a null-terminated sequence of characters.

String operator + (const String &x, const String &y)

Concatenates a String object with another String object.

String &operator = (const char *s)

Assigns a String object to a null-terminated sequence of characters.

String &operator = (const String &x)

Assigns a String object to another String object.

int operator < (const char *s, const String &x)

Tests if a null-terminated sequence of characters is less than a String object; if so, it returns 1. Otherwise, it returns 0.

int operator < (const String &x, const char *s)

Tests if a String object is less than a null-terminated sequence of characters; if so, it returns 1. Otherwise, it returns 0.

int operator < (const String &x, const String &y)

Compares two String objects to determine if the first is less than the second; if so, it returns 1. Otherwise, it returns 0.

int operator > (const char *s, const String &x)

Tests if a null-terminated sequence of characters is greater than a String object; if so, it returns 1. Otherwise, it returns 0.

int operator > (const String &x, const char *s)

Tests if a String object is greater than a null-terminated sequence of characters; if so, it returns 1. Otherwise, it returns 0.

int operator > (const String &x, const String &y)

Compares two String objects to determine if the first is greater than the second; if so, it returns 1. Otherwise, it returns 0.

String &operator += (const char *st2)

Concatenates a null-terminated sequence of characters to a String object.

String &operator += (const String &st2)

Concatenates a String object to another String object.

ostream &operator << (ostream &s, const String &x)

Inserts the sequence of characters represented by x into the stream s.

istream &operator >> (istream &s, String &x)

Extracts characters from s using the istream extraction operator, then stores characters in x, replacing the current contents of x and dynamically allocating x as necessary.

int operator :=,= (const char *s, const String &x)

Tests if a null-terminated sequence of characters is equal to a String object; if so, it returns 1. Otherwise, it returns 0.

int operator :=,= (const String &x, const char *s)

Tests if a String object is equal to a null-terminated sequence of characters; if so, it returns 1. Otherwise, it returns 0.

int operator :=,= (const String &x, const String &y)

Compares two String objects to determine equality. If one is equal to the other, it returns 1; otherwise, it returns 0.

int operator != (const char *s, const String &x)

Tests if a null-terminated sequence of characters is not equal to a String object; if so, it returns 1. Otherwise, it returns 0.

int operator != (const String &x, const char *s)

Tests if a String object is not equal to a null-terminated sequence of characters; if so, it returns 1. Otherwise, it returns 0.

int operator != (const String &x, const String &y)

Compares two String objects to determine inequality. If they are not equal, the function returns 1; otherwise, it returns 0.

int operator <= (const char *s, const String &x)

Tests if a null-terminated sequence of characters is less than or equal to a String object; if so, it returns 1. Otherwise, it returns 0.

int operator <= (const String &x, const char *s)

Tests if a String object is less than or equal to a null-terminated sequence of characters; if so, it returns 1. Otherwise, it returns 0.

int operator <= (const String &x, const String &y)

Compares two String objects to determine if the first is less than or equal to the second; if so, it returns 1. Otherwise, it returns 0.

int operator >= (const char *s, const String &x)

Tests if a null-terminated sequence of characters is equal to or greater than a String object; if so, it returns 1. Otherwise, it returns 0.

int operator >= (const String &x, const char *s)

Tests if a String object is equal to or greater than a null-terminated sequence of characters; if so, it returns 1. Otherwise, it returns 0.

int operator >= (const String &x, const String &y)

Compares two String objects to determine if the first is equal to or greater than the second; if so, it returns 1. Otherwise, it returns 0.

String operator () (int index, int count) const

Creates a new String object defined as a substring of the current String, with index as the starting character and count as the length of the substring.

char operator [] (int position) const

Returns the character at the requested position within the string. If the position is past the end of the string, it returns 0. If the position is negative, the results are undefined.

char &operator [] (int position)

Returns a reference to the character at the requested position within the string. This reference is potentially invalid after any subsequent call to a non-const member function for the object. If the position is past the end of the string or if the position is negative, the results are undefined.

Other Member Functions

int index(const String &x) const

Returns the index value of the first position where an element of a String object coincides with the value of x.

unsigned int length() const

Returns the length (number of characters) in a String object.

String lower() const

Returns a new String object constructed from a String except that every character is lowercase regardless of its original case.

int match(const String &x) const

Compares two strings and returns the first index position at which they differ; it returns --1 if the strings match completely. The String argument can be a character pointer.

String upper() const

Returns a new String constructed from a String except that every character is uppercase regardless of its original case.

Examples

String x ("The Times of John Doe"); 
char *y = "Pink Triangles"; 
 
if (x != y) cout << "We have two different strings.\n"; 
 
x = y; 
 
cout << x; 
 
      

The first line of this example provides a character string to the constructor for initialization. The overloaded operators (!=, <<, and =) accept either two String objects or a String and a null-terminate sequence of characters. The last line prints out the following character string:

Pink Triangles

String x ("The Times of John Doe"); 
 
String a (x(18,3));    // Substring is "Doe" 
String b (x);          // b contains all of x 
 
      

In this example, the creation of object a provides a substring of object x to the constructor for object a. The substring begins at position 18 and has a length of 3 characters. The next line creates the object b and initializes it to contain the same value as x.

String x ("World"); 
String y; 
 
y = "Hello"; 
y += ", " + x + ".\n";      
 
cout << y;  
 
      

---

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