Computer Select (Limited Edition)/Computer Select.iso/dobbs/v16n10/stringcl.asc

Text File | 1991-09-10 | 9.0 KB | 361 lines

_PROPOSING A C++ STRING CLASS_
by Steve Teale

[LISTING ONE]


class String {
public:
// String class constants
    enum string_enum { all = INT_MAX };

// Constructors / destructor
    String();                // make an empty String
    String(const String&);       // make a String by copying another
    String(const char *, int count = 0);
                                 // make a String from a regular C style string
    String(char);            // make a String from a single char

    ~String();             // Clean up after a String goes out of scope

// Assignments
    String &operator=(const String&);   // Assign from another String
    String &operator=(const char *);    // Assign from a C style string
    String &operator=(char);        // Assign from a single char
    String &operator+=(const String&);
                                  // Concatenate a String to an existing String
    String &operator+=(const char *);
                                    // Concatenate a C style string to a String
    String &operator+=(char);       // Concatenate a char

// Other modifiers
    String &insert(int pos, const String&);  // Insert into an existing string
    String &insert(int pos, const char *);
    String &insert(int pos, char);
    String &remove(int pos, int count); // Remove from an existing string
    String &truncate(int);      // Truncate a String

// Conversions
    operator char*() const;
                     // Translate a String to a pointer to its first character
    operator char() const;     // Translate a String to its initial character

// Mutators (make an existing String into a variant)
    String upper() const;      // Make a new String by conversion to uppercase
    String lower() const;
    String operator()(int start, int len);
                   // Make a new String starting from start, of len characters

// Access individual characters
    char &operator[](int);    // Access individual characters as if the String
                  // were an array
    char operator()(int);     // Get the character value of the i'th character.

// Searches
    int match(const String&) const;
è                             // Return position of first non-matching character
    int match(const char *) const;
    int index(const String&, int pos = 0) const;
    int index(const char *, int = 0) const;
                             // Find the position of a substring or character
    int index(char, int = 0) const;

// Statistics
    int operator!() const;  // Test for an empty string
    int length() const;     // Get the length of the String

// Some of the properties of a String are provided by functions which
// are friends of the String class

friend int strlen(const String&);   // Parallel the ANSI C string functions
// etc

// Concatenations to make a new String
friend String operator+(const String&, const String&);
friend String operator+(const String&, const char *);
friend String operator+(const char *, const String&);

// Boolean tests
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&);

// Input/ output operations
friend istream &operator>>(istream&, String&);
friend ostream &operator<<(ostream&, const String&);
};


[LISTING TWO]


#ifndef __STRING_HPP
#define __STRING_HPP
#include <limits.h>

èclass istream;   // forward declarations to avoid including all of iostream.hpp
class ostream;

class srep {        // actual string representation
friend class String;
private:
    srep(int, const char * = 0);
    void *operator new(size_t cs, size_t ss = 0);

    int refs;
    int length;
    char body[1];
};

class String {
public:
    // as above
private:
    char *body() const { return rp? rp->body: 0; }

    srep *rp;
    static char dummy;
};

inline int strlen(const String &s)
{
    return s.length();
}

// and other friend functions which can conveniently be defined inline

#endif




Figurσ 1

(a)

    String &operator=(char);
    String &operator+=(char);

    String &insert(int, const String&);
    String &insert(int, const char *);
    String &insert(int, char);
    String &remove(int, int);

    int operator!();


(b)

String a;

èif (!a) ...;        // if a is empty string
if (a) ...;     // if a is not empty - uses operator char *()


(c)

friend int operator==(const String&, const String&);
friend int operator==(const String&, const char *);
friend int operator==(const char *, const String&);







Figure 2

(a)

    String a;
    ...
    if (a == "whatever")
        ...;

will cause a sequence something like:

    String temp = "whatever";   // constructor from const char *
    if (operator==(a, temp))
        ...;
    // temp destructor call


(b)

// two members
    int operator==(const String&);
    int operator==(const char *);

// and a friend
friend int operator==(const char *, const String&);




Figure 3


(a)

String t;           // an empty string
String a  = "good girl";    // initialized from a regular C style string
String b = a;       // the copy constructor
String c = '.';

èThis is the idiomatic usage.  It would have just the same effect to write:

String a("good girl");
String b(a);
String c('.');


(b)


String d("good girl", 4);
// same effect as String d = "good";


(c)


String v = "abcd";
v += 1;         // result "bcde" ?

String w = "provided"
w  -= "vide"        // result "prod" ?
w -= 'r';           // result "pod"   ?

String x = "1234567890"
x <<= 1;            // result "2345678901"




Figure 4

(a)


    operator char();    // conversion to a char
    operator char *();  // conversion to a char *

(b)

    void show(char c)
    {
        cout << c << ' ' << int(c) << endl;
    }

    char array[4] = { '\0', '\0', '\0', '\0' };

    String nulls(array,4);
    String empty;

    show(nulls);
    show(empty);



èFigure 5

(a)

    String String::upper() const;
    String String::lower() const;
    String String::operator()(int start, int length) const;
    String operator+(const String &a, const String &b);
    String operator+(const String &a, const char *b);
    String operator+(const char *a, const String &b);


(b)


    String a = "Cat";
    a(0) = 'R';         // a gets "Rat"
    // a.operator()(0) = 'R';




Figure 6

(a)

String a = "The quick brown fox jumped over the lazy dogs back";
String b = "The queen";
String c = "lazy";

a.match(b);         // returns 7
a.match("The quick");       // returns -1

a.index(b);         // returns -1
a.index(c);         // returns 36
a.index("The", 1);      // returns -1
a.index("The");         // returns 0
a.index("the");         // returns 32
a.index('b');           // returns 10
a.index('b',11);            // returns 46


(b)


// C style
    char *s1 = "Joe", *s2 = "Fred";
    if (s1 > s2) ...;           // legal, but not usually what was intended!
    if (!strcmp(s1,s2)) ...;        // proper test for equality

// C++ style

    String s1 = "Joe", s2 = "Fred";
    if (s1 > s2) ...;           // evaluates to true
    if (s1 == s2) ...;          // proper test for equality


Figure 6

(a)

String a = "The quick brown fox jumped over the lazy dogs back";
String b = "The queen";
String c = "lazy";

a.match(b);         // returns 7
a.match("The quick");       // returns -1

a.index(b);         // returns -1
a.index(c);         // returns 36
a.index("The", 1);      // returns -1
a.index("The");         // returns 0
a.index("the");         // returns 32
a.index('b');           // returns 10
a.index('b',11);            // returns 46


(b)


// C style
    char *s1 = "Joe", *s2 = "Fred";
    if (s1 > s2) ...;           // legal, but not usually what was intended!
    if (!strcmp(s1,s2)) ...;        // proper test for equality

// C++ style

    String s1 = "Joe", s2 = "Fred";
    if (s1 > s2) ...;           // evaluates to true
    if (s1 == s2) ...;          // proper test for equality