1.  2000 Deitel & Associates, Inc. All rights reserved. Chapter 19 - Class string and Stream Processing Outline 19.1Introduction 19.2 string Assignment and Concatenation 19.3Comparing strings 19.4Substrings 19.5Swapping string s 19.6 string Characteristics 19.7Finding Characters in a string 19.8Replacing Characters in a string 19.9Inserting Characters into a string 19.10Conversion to C-Style char * Strings 19.11Iterators 19.12String Stream Processing

2.  2000 Deitel & Associates, Inc. All rights reserved. 19.1Introduction template class basic_string –typedef basic_string string; creates alias string for basic_string which we use –include Initialization –string s1( "Hi"); –string s2( 8, 'x'); –string name = "Jim"; not truly assignment, calls copy constructor WRONG: string s1 = 'c'; string s2( 'u' ); string s3 = 34; string s4( 8 ); no automatic conversion between int or char to string

3.  2000 Deitel & Associates, Inc. All rights reserved. 19.1Introduction (II) string s do not always end in '\0' use the [] operator to access elements –first subscript 0 –string not a pointer. &string1[0] != string1 String length - s1.size() or s1.length() Inputting strings string myString; cin >> myString; delimited by whitespace characters string myString; getline(cin, myString); overloaded getline function delimited by newline ( '\n' )

4.  2000 Deitel & Associates, Inc. All rights reserved. 19.2 string Assignment and Concatenation String assignment –= operator: s2 = s1; –assign(): s2.assign(s1); copies s1 into s2 –s2.assign(s1, startSubscript, numberOfChars); copies numberOfChars characters in s1 to s2, starting from startSubscript –s2[0] = 'm'; sets first character of s2 to 'm'

5.  2000 Deitel & Associates, Inc. All rights reserved. 19.2 string Assignment and Concatenation (II) More string operations –s2.at(2); range checked access –s2 += "hi" concatenates s2 and "hi" –s2.append("_again"); concatenates "_again" and s2 –s2.append(s1, startSubscript, numberOfChars); concatenates numberOfChars characters in s1 with s2, starting from startSubscript

6.  2000 Deitel & Associates, Inc. All rights reserved. Outline 1. Initialize string s 2. Modify string s 3. Print string s 1// Fig. 19.1: fig19_01.cpp 2// Demonstrating string assignment and concatenation 3#include 4 5using std::cout; 6using std::endl; 7 8#include 9 10using std::string; 11 12int main() 13{ 14 string s1( "cat" ), s2, s3; 15 16 s2 = s1; // assign s1 to s2 with = 17 s3.assign( s1 ); // assign s1 to s3 with assign() 18 cout << "s1: " << s1 << "\ns2: " << s2 << "\ns3: " 19 << s3 << "\n\n"; 20 21 // modify s2 and s3 22 s2[ 0 ] = s3[ 2 ] = 'r'; 23 24 cout << "After modification of s2 and s3:\n" 25 << "s1: " << s1 << "\ns2: " << s2 << "\ns3: "; 26 27 // demonstrating member function at() 28 int len = s3.length(); 29 for ( int x = 0; x < len; ++x ) 30 cout << s3.at( x ); 31 32 // concatenation s1: cat s2: cat s3: cat After modification of s2 and s3: s1: cat s2: rat s3: car

7.  2000 Deitel & Associates, Inc. All rights reserved. Outline 3. Print string s Program Output 33 string s4( s1 + "apult" ), s5; // declare s4 and s5 34 35 // overloaded += 36 s3 += "pet"; // create "carpet" 37 s1.append( "acomb" ); // create "catacomb" 38 39 // append subscript locations 4 thru the end of s1 to 40 // create the string "comb" (s5 was initially empty) 41 s5.append( s1, 4, s1.size() ); 42 43 cout << "\n\nAfter concatenation:\n" << "s1: " << s1 44 << "\ns2: " << s2 << "\ns3: " << s3 << "\ns4: " << s4 45 << "\ns5: " << s5 << endl; 46 47 return 0; 48} s1: cat s2: cat s3: cat After modification of s2 and s3: s1: cat s2: rat s3: car After concatenation: s1: catacomb s2: rat s3: carpet s4: catapult s5: comb After concatenation: s1: catacomb s2: rat s3: carpet s4: catapult s5: comb

8.  2000 Deitel & Associates, Inc. All rights reserved. 19.3Comparing strings overloaded ==, !=,, = operators –for string comparisons –return bool values result = s1.compare(s2); –lexicographical comparison –if s1 > s2, result > 0 –if s1 < s2, result < 0 –if s1 == s2, result = 0 s1.compare(sub1, sub2, s2, sub3, sub4) compares s1 from subscript sub1 to sub2 with s2 from subscript sub3 to sub4. s1.compare(sub1, number, s2) compares number characters in s1 starting from subscript sub1 with s2.

9.  2000 Deitel & Associates, Inc. All rights reserved. Outline 1. Initialize string s 2. Compare string s 1// Fig. 19.2: fig19_02.cpp 2// Demonstrating string comparison capabilities 3#include 4 5using std::cout; 6using std::endl; 7 8#include 9 10using std::string; 11 12int main() 13{ 14 string s1( "Testing the comparison functions." ), 15 s2("Hello" ), s3( "stinger" ), z1( s2 ); 16 17 cout << "s1: " << s1 << "\ns2: " << s2 18 << "\ns3: " << s3 << "\nz1: " << z1 << "\n\n"; 19 20 // comparing s1 and z1 21 if ( s1 == z1 ) 22 cout << "s1 == z1\n"; 23 else { // s1 != z1 24 if ( s1 > z1 ) 25 cout z1\n"; 26 else // s1 < z1 27 cout << "s1 < z1\n"; 28 } 29 30 // comparing s1 and s2 31 int f = s1.compare( s2 ); 32 33 if ( f == 0) s1: Testing the comparison functions. s2: Hello s3: stinger z1: Hello s1 > z1

10.  2000 Deitel & Associates, Inc. All rights reserved. Outline 2. Compare string s 34 cout << "s1.compare( s2 ) == 0\n"; 35 else if ( f > 0 ) 36 cout 0\n"; 37 else // f < 0 38 cout << "s1.compare( s2 ) < 0\n"; 39 40 // comparing s1 (elements 2 - 5) and s3 (elements 0 - 5) 41 f = s1.compare( 2, 5, s3, 0, 5 ); 42 43 if ( f == 0 ) 44 cout << "s1.compare( 2, 5, s3, 0, 5 ) == 0\n"; 45 else if ( f > 0 ) 46 cout 0\n"; 47 else // f < 0 48 cout << "s1.compare( 2, 5, s3, 0, 5 ) < 0\n"; 49 50 // comparing s2 and z1 51 f = z1.compare( 0, s2.size(), s2 ); 52 53 if ( f == 0 ) 54 cout << "z1.compare( 0, s2.size(), s2 ) == 0" << endl; 55 else if ( f > 0 ) 56 cout 0" << endl; 57 else // f < 0 58 cout << "z1.compare( 0, s2.size(), s2 ) < 0" << endl; 59 60 return 0; 61} s1.compare( s2 ) > 0 s1.compare( 2, 5, s3, 0, 5 ) == 0 z1.compare( 0, s2.size(), s2 ) == 0

11.  2000 Deitel & Associates, Inc. All rights reserved. Outline Program Output s1: Testing the comparison functions. s2: Hello s3: stinger z1: Hello s1 > z1 s1.compare( s2 ) > 0 s1.compare( 2, 5, s3, 0, 5 ) == 0 z1.compare( 0, s2.size(), s2 ) == 0

12.  2000 Deitel & Associates, Inc. All rights reserved. 19.4Substrings Function substr retrieves a substring from a string. s1.substr( startSubScript, number ); –startSubscript - starting subscript –number - number of characters to extract –returns the substring

13.  2000 Deitel & Associates, Inc. All rights reserved. 19.5Swapping string s Function swap swaps the contents of two string s. s1.swap(s2); –switches s1 and s2

14.  2000 Deitel & Associates, Inc. All rights reserved. 19.6 string Characteristics s1.size() and s1.length() – current number of characters in string s1.capacity() –number of elements that can be stored without reallocation s1.max_size() –maximum possible string size str.empty() –if no characters, returns true s1.resize(newlength) –resizes string to newlength

15.  2000 Deitel & Associates, Inc. All rights reserved. Outline 1. Initialize string 2. Function calls 3. Output 1// Fig. 19.5: fig19_05.cpp 2// Demonstrating functions related to size and capacity 3#include 4 5using std::cout; 6using std::endl; 7using std::cin; 8 9#include 10 11using std::string; 12 13void printStats( const string & ); 14 15int main() 16{ 17 string s; 18 19 cout << "Stats before input:\n"; 20 printStats( s ); 21 22 cout << "\n\nEnter a string: "; 23 cin >> s; // delimited by whitespace 24 cout << "The string entered was: " << s; 25 26 cout << "\nStats after input:\n"; 27 printStats( s ); 28 29 s.resize( s.length() + 10 ); 30 cout << "\n\nStats after resizing by (length + 10):\n"; 31 printStats( s ); 32 33 cout << endl; Stats before input: capacity: 0 max size: 4294967293 size: 0 length: 0 empty: true Enter a string: tomato soup The string entered was: tomato Stats after input: capacity: 31 max size: 4294967293 size: 6 length: 6 empty: false Stats after resizing by (length + 10): capacity: 31 max size: 4294967293 size: 16 length: 16 empty: false

16.  2000 Deitel & Associates, Inc. All rights reserved. Outline 3.1 Function definition Program Output 34 return 0; 35} 36 37void printStats( const string &str ) 38{ 39 cout << "capacity: " << str.capacity() 40 << "\nmax size: " << str.max_size() 41 << "\nsize: " << str.size() 42 << "\nlength: " << str.length() 43 << "\nempty: " << ( str.empty() ? "true": "false" ); 44} Stats before input: capacity: 0 max size: 4294967293 size: 0 length: 0 empty: true Enter a string: tomato soup The string entered was: tomato Stats after input: capacity: 31 max size: 4294967293 size: 6 length: 6 empty: false Stats after resizing by (length + 10): capacity: 31 max size: 4294967293 size: 16 length: 16 empty: false

17.  2000 Deitel & Associates, Inc. All rights reserved. 19.7Finding Characters in a string Class string find functions: –if found, subscript of match returned –if not found, value of string::npos is returned – s1.find(string) - searches s1 for string – s1.rfind(string) - like find, but searches s1 for string backwards. – s1.find_first_of(string) - finds first occurrence in s1 of any character in string – s1.find_last_of(string) - as above, but last occurrence. Searches s1 backwards. – s1.find_first_not_of(string)- finds first character in s1 NOT in s2. – s1.find_last_not_of(string) - as above, but last character. Searches s1 backwards.

18.  2000 Deitel & Associates, Inc. All rights reserved. Outline 1. Initialize string 2. Function calls 3. Output 1// Fig. 19.6: fig19_06.cpp 2// Demonstrating the string find functions 3#include 4 5using std::cout; 6using std::endl; 7 8#include 9 10using std::string; 11 12int main() 13{ 14 // compiler concatenates all parts into one string literal 15 string s( "The values in any left subtree" 16 "\nare less than the value in the" 17 "\nparent node and the values in" 18 "\nany right subtree are greater" 19 "\nthan the value in the parent node" ); 20 21 // find "subtree" at locations 23 and 102 22 cout << "Original string:\n" << s 23 << "\n\n(find) \"subtree\" was found at: " 24 << s.find( "subtree" ) 25 << "\n(rfind) \"subtree\" was found at: " 26 << s.rfind( "subtree" ); 27 28 // find 'p' in parent at locations 62 and 144 29 cout << "\n(find_first_of) character from \"qpxz\" at: " 30 << s.find_first_of( "qpxz" ) 31 << "\n(find_last_of) character from \"qpxz\" at: " 32 << s.find_last_of( "qpxz" ); 33 Original string: The values in any left subtree are less than the value in the parent node and the values in any right subtree are greater than the value in the parent node (find) "subtree" was found at: 23 (rfind) "subtree" was found at: 102 (find_first_of) character from "qpxz" at: 62 (find_last_of) character from "qpxz" at: 144

19.  2000 Deitel & Associates, Inc. All rights reserved. Outline 3. Output Program Output 34 // find 'b' at location 25 35 cout << "\n(find_first_not_of) first character not\n" 36 << " contained in \"heTv lusinodrpayft\": " 37 << s.find_first_not_of( "heTv lusinodrpayft" ); 38 39 // find '\n' at location 121 40 cout << "\n(find_last_not_of) first character not\n" 41 << " contained in \"heTv lusinodrpayft\": " 42 << s.find_last_not_of( "heTv lusinodrpayft" ) << endl; 43 44 return 0; 45} Original string: The values in any left subtree are less than the value in the parent node and the values in any right subtree are greater than the value in the parent node (find) "subtree" was found at: 23 (rfind) "subtree" was found at: 102 (find_first_of) character from "qpxz" at: 62 (find_last_of) character from "qpxz" at: 144 (find_first_not_of) first character not contained in "heTv lusinodrpayft": 25 (find_last_not_of) first character not contained in "heTv lusinodrpayft": 121 (find_first_not_of) first character not contained in "heTv lusinodrpayft": 25 (find_last_not_of) first character not contained in "heTv lusinodrpayft": 121

20.  2000 Deitel & Associates, Inc. All rights reserved. 19.8Replacing Characters in a string s1.erase(number); –erases everything after element number to the end s1.replace(sub1, numberToReplace, replacementString, sub2, numberToUse); –sub1 - subscript in s1 where replacement occurs –numberToReplace - number of characters being replaced in s1, starting from sub1 –replacementString - string containing replacement characters –sub2 - beginning subscript of replacement characters in replacementString –numberToUse - number of replacement characters to use in replacementString, starting with sub2

21.  2000 Deitel & Associates, Inc. All rights reserved. Outline 1. Initialize string 2. Function calls 3. Output 1// Fig. 19.7: fig19_07.cpp 2// Demonstrating functions erase and replace 3#include 4 5using std::cout; 6using std::endl; 7 8#include 9 10using std::string; 11 12int main() 13{ 14 // compiler concatenates all parts into one string 15 string s( "The values in any left subtree" 16 "\nare less than the value in the" 17 "\nparent node and the values in" 18 "\nany right subtree are greater" 19 "\nthan the value in the parent node" ); 20 21 // remove all characters from location 62 22 // through the end of s 23 s.erase( 62 ); 24 25 // output the new string 26 cout << "Original string after erase:\n" << s 27 << "\n\nAfter first replacement:\n"; 28 29 // replace all spaces with a period 30 int x = s.find( " " ); 31 while ( x < string::npos ) { 32 s.replace( x, 1, "." ); 33 x = s.find( " ", x + 1 ); Original string after erase: The values in any left subtree are less than the value in the Remove all characters from location 62 (the 63rd element) to the end. After first replacement: The.values.in.any.left.subtree are.less.than.the.value.in.the

22.  2000 Deitel & Associates, Inc. All rights reserved. Outline 3. Output Program Output 34 } 35 36 cout << s << "\n\nAfter second replacement:\n"; 37 38 // replace all periods with two semicolons 39 // NOTE: this will overwrite characters 40 x = s.find( "." ); 41 while ( x < string::npos ) { 42 s.replace( x, 2, "xxxxx;;yyy", 5, 2 ); 43 x = s.find( ".", x + 1 ); 44 } 45 46 cout << s << endl; 47 return 0; 48} Original string after erase: The values in any left subtree are less than the value in the After first replacement: The.values.in.any.left.subtree are.less.than.the.value.in.the After second replacement: The;;alues;;n;;ny;;eft;;ubtree are;;ess;;han;;he;;alue;;n;;he After second replacement: The;;alues;;n;;ny;;eft;;ubtree are;;ess;;han;;he;;alue;;n;;he

23.  2000 Deitel & Associates, Inc. All rights reserved. 19.9Inserting Characters into a string s1.insert(sub1, string) –inserts string before element sub1 in s1 s1.insert(sub1, string, sub2, numChars); –selects numChars characters, starting from sub2 in string, and inserts them into s1.

24.  2000 Deitel & Associates, Inc. All rights reserved. 19.10 Conversion to C-Style char * Strings string s can be converted to C-style char * strings –s1.data() - conversion to const char * string, not null terminated –s1.c_str() - conversion to const char * string, null terminated (ends with '\0' )

25.  2000 Deitel & Associates, Inc. All rights reserved. Outline 1. Initialize string s 2. Insert string s 3. Print results. 1// Fig. 19.9: fig19_09.cpp 2// Converting to C-style strings. 3#include 4 5using std::cout; 6using std::endl; 7 8#include 9 10using std::string; 11 12int main() 13{ 14 string s( "STRINGS" ); 15 const char *ptr1 = 0; 16 int len = s.length(); 17 char *ptr2 = new char[ len + 1 ]; // including null 18 19 // copy characters out of string into allocated memory 20 s.copy( ptr2, len, 0 ); 21 ptr2[ len ] = 0; // add null terminator 22 23 // output 24 cout << "string s is " << s 25 << "\ns converted to a C-Style string is " 26 << s.c_str() << "\nptr1 is "; 27 28 // Assign to pointer ptr1 the const char * returned by 29 // function data(). NOTE: this is a potentially dangerous 30 // assignment. If the string is modified, the pointer 31 // ptr1 can become invalid. 32 ptr1 = s.data(); 33 Notice the format for inserting strings. string s is STRINGS s converted to a C-Style string is STRINGS ptr1 is STRINGS

26.  2000 Deitel & Associates, Inc. All rights reserved. Outline 3. Print results. Program Output 34 for ( int k = 0; k < len; ++k ) 35 cout << *( ptr1 + k ); // use pointer arithmetic 36 37 cout << "\nptr2 is " << ptr2 << endl; 38 delete [] ptr2; 39 return 0; 40} string s is STRINGS s converted to a C-Style string is STRINGS ptr1 is STRINGS ptr2 is STRINGS

27.  2000 Deitel & Associates, Inc. All rights reserved. 19.11 Iterators iterators –forwards and backwards traversal of strings –access to individual characters –similar to pointer operations Basic coverage here - more next chapter –type const_iterator - iterator that cannot modify the string –s.begin() - returns iterator to front of string –s.end() - returns iterator to end –*myIterator - dereferences iterator (like pointer) –++myIterator - advances iterator one position (character)

28.  2000 Deitel & Associates, Inc. All rights reserved. 19.12 String Stream Processing in-memory I/O (string stream processing) –headers and Inputting strings to memory –create objects of class istringstream istringstream myInputString; –works the same as input from a file –can feed input string into other strings Output to a string –objects of class ostringstream ostringstream myOutputString; - myOutputString.str() - outputs the string

29.  2000 Deitel & Associates, Inc. All rights reserved. Outline 1. Initialize ostringstream object 1.1 Initialize string s 1.2 Initialize variables 2. Print outputString 2.1 Modify outputString 1// Fig. 19.11: fig19_11.cpp 2// Using a dynamically allocated ostringstream object. 3#include 4 5using std::cout; 6using std::endl; 7 8#include 9 10using std::string; 11 12#include 13 14using std::ostringstream; 15 16int main() 17{ 18 ostringstream outputString; 19 string s1( "Output of several data types " ), 20 s2( "to an ostringstream object:" ), 21 s3( "\n double: " ), 22 s4( "\n int: " ), 23 s5( "\naddress of int: " ); 24 double d = 123.4567; 25 int i = 22; 26 27 outputString << s1 << s2 << s3 << d << s4 << i << s5 << &i; 28 cout << "outputString contains:\n" << outputString.str(); 29 30 outputString << "\nmore characters added"; output string s to outputString outputString contains: Output of several data types to an ostringstream object: double: 123.457 int: 22 address of int: 0068FD0C Add more characters to outputString

30.  2000 Deitel & Associates, Inc. All rights reserved. Outline 2.2 Print outputString Program Output 31 cout << "\n\nafter additional stream insertions,\n" 32 << "outputString contains:\n" << outputString.str() 33 << endl; 34 35 return 0; 36} outputString contains: Output of several data types to an ostringstream object: double: 123.457 int: 22 address of int: 0068FD0C after additional stream insertions, outputString contains: Output of several data types to an ostringstream object: double: 123.457 int: 22 address of int: 0068FD0C more characters added after additional stream insertions, outputString contains: Output of several data types to an ostringstream object: double: 123.457 int: 22 address of int: 0068FD0C more characters added

31.  2000 Deitel & Associates, Inc. All rights reserved. Outline 1. Initialize objects 2. Input data into string1 and string2 1// Fig. 19.12: fig19_12.cpp 2// Demonstrating input from an istringstream object. 3#include 4 5using std::cout; 6using std::endl; 7 8#include 9 10using std::string; 11 12#include 13 14using std::istringstream; 15 16int main() 17{ 18 string input( "Input test 123 4.7 A" ); 19 istringstream inputString( input ); 20 string string1, string2; 21 int i; 22 double d; 23 char c; 24 25 inputString >> string1 >> string2 >> i >> d >> c; 26 27 cout << "The following items were extracted\n" 28 << "from the istringstream object:" 29 << "\nstring: " << string1 30 << "\nstring: " << string2 31 << "\n int: " << i 32 << "\ndouble: " << d 33 << "\n char: " << c; Notice how inputString inputs data to string1 and string2 (similar format as cin ) The following items were extracted from the istringstream object: String: Input String: test int: 123 double: 4.7 char: A

32.  2000 Deitel & Associates, Inc. All rights reserved. Outline 2. Function calls Program Output 34 35 // attempt to read from empty stream 36 long x; 37 38 inputString >> x; 39 40 if ( inputString.good() ) 41 cout << "\n\nlong value is: " << x << endl; 42 else 43 cout << "\n\ninputString is empty" << endl; 44 45 return 0; 46} The following items were extracted from the istringstream object: String: Input String: test int: 123 double: 4.7 char: A inputString is empty