C Strings oops with c++ ppt or pdf can be done.pdf

Creating String Objects
C-string
C++ string
Array of chars that is null terminated (‘0’).
• Object whose string type is defined in the <string> file
• Has a large repertoire of functions (e.g. length, replace, etc.)
char cs[ ] = “Napoleon”; // C-string
string s = “Napoleon”; // C++ string
cout << s << “ has “ << s.length() << “ characters.n”;
s.replace(5, 2,”ia”); //changes s to “Napolian

Formatted Input: Stream extraction operator
• cin >> stringObject;
• the extraction operator >> formats the data that it receives through its input
stream; it skips over whitespace
Unformatted Input: getline function for a string
• getline( cin, s)
• does not skip over whitespace
• delimited by newline
• reads an entire line of characters into s
• string s = “ABCDEFG”;
• getline(cin, s); //reads entire line of characters into s
• char c = s[2]; //assigns ‘C’ to c
• S[4] = ‘*’; //changes s to “ABCD*FG”

• Not necessarily null terminated
• string is not a pointer, but a class
STRINGS

#include <string>
//string initialization
string s; //s contains 0 characters
string s1( "Hello" ); //s1 contains 5 characters
string s2 = “Hello”; //s2 contains 5 characters
//implicitly calls the constructor
string s3( 8, 'x' ); //s3 contains 8 'x' characters
string s4 = s3; //s4 contains 8 'x' characters
string s5(s2, 3, 2); //s5 copies a substring of s2; it contains ”l0”
string type in the <string> header file.
Creating String Objects

string s = “ABCDEFG”;
const char* cs = s.c_str(); Converts s into the C-string cs.
C++ strings can be converted to C-strings:
The c_str() function has a return type const char*
String Objects

cout << s.length() << endl;
Prints 4 for the string s == “Blue”
The C++ string class also defines a length() function for extracting how
many characters are stored in a string.
You can also use the subscript operator [ ] to access individual
characters:
e.g. s[0] = ‘N’ ; //where index: 0 to length-1
String Objects

If (s2 < s5)
cout << “s2 lexicographically precedes s5 n”;
while(s4==s3) //…
'B' is lexicographically greater than 'A'
C++ strings can be compared using relational operators just like
fundamental types:
Sample order: ‘A’,”Apple”, “Banana”, “Zest”, ‘a’, “apricot”
String Objects

string s = “ABCD*FG”;
string s2 = “MIT”;
string s5 = “Manipal”;
string s6 = s + “HIJK”; //changes s6 to “ABCD*FGHIJK
s2 += s5; //changes s2 to “MITManipal”
You can also concatenate C++ strings using the + and +=
operators:
String Objects

s6 = “ABCD*FGHIJK”;
s4 = s6.substr(5, 3); //changes
s4 to “FGH”
Substring function: substr()
s4 gets a substring of s6, starting at index 5 and taking 3
characters
String Objects

s6 = “ABCD*FGHIJK”;
s6.erase(4, 2); //changes s6 to “ABCDGHIJK”;
s6.replace(5, 2, “xyz”); //changes s6 to “ABCDGxyzJK”;
erase() and replace() functions:
replace 2 characters from s6, starting at index 5, with “xyz”
String Objects

string s7 = “Mississippi River basin”; //23 characters
cout << s7.find(“si”) << endl; //prints 3
cout << s7.find(“so”) << endl; //prints 23, the length of the string
find() function:returns the index of the first occurrence of a given
substring:
If the find() function fails, it returns the length of the string it was
searching.
String Objects

Assignment in strings
s2 = s1; Makes a separate copy
s2.assign(s1); Same as s2 = s1;
myString.assign(s, start, N); Copies N characters from s,
beginning at index start
Individual character assignment s2[0] = s3[2];

Range-checking
s3.at( index ); Returns character at index
Can throw an out_of_range exception
[ ] has no range checking
#include <exception>
...
string s = “blue";
try{
char letter = s.at( 50 );
cout <<"letter is = " << letter << endl;
}
catch(exception& e){
cout << "out_of_range exception: " << endl;
}

Concatenation
s3.append( “MIT" );
s3 += “MIT"; Both add “MIT" to end of s3
s3.append( s1, start, N ); Appends N characters from s1,
beginning at index start

Comparing strings
• Overloaded operators
– ==, !=, <, >, <= and >=
– returns bool
• s1.compare(s2)
– returns positive if s1 is lexicographically greater
• compares letter by letter
• 'B' lexicographically greater than 'A‘
• ‘a’ lexicographically greater than ‘A‘
• ‘a’ lexicographically greater than ‘Z‘
– returns negative if less; zero if equal
• Sample order: ‘A’,”Apple”, “Banana”, “Zest”, ‘a’, “apricot”, “pear”
– s1.compare(start, length, s2, start, length)
• Compare portions of s1 and s2
– s1.compare(start, length, s2)
• Compare portion of s1 with all of s2

Substrings
Function substr gets a substring
s1.substr( start, N );
gets N characters, beginning with index start and returns
substring

Swapping strings
s1.swap(s2);
switches contents of two strings

Finding Strings and Characters in a string
Find functions: If found, index returned
If not found, string::npos returned
s1.find( s2 )
s1.rfind( s2 ) Searches right-to-left
s1.find_first_of( s2 ) Returns first occurrence of any character
in s2
Example: s1.find_first_of( "abcd" )
Returns index of first 'a', 'b', 'c' or 'd'

Finding Strings and Characters in a string
Find functions
s1.find_last_of( s2 ) Finds last occurrence of any
character in s2
s1.find_first_not_of( s2 ) Finds first character NOT in s2
s1.find_last_not_of( s2 ) Finds last character NOT in s2

Replacing Characters in a string
s1.erase( start ) Erase from index start to end of string, including start
s1.replace( begin, N, s2) begin: index in s1 to start replacing
N: number of characters to replace
s2: replacement string
s1.replace( begin, N, s2, index, num )
• index: element in s2 where replacement comes from
• num: number of elements to use when replacing
Replace can overwrite characters

Example
s1.replace( begin, N, s2, index, num )
• begin: index in s1 to start replacing
• N: number of characters to replace
• s2: replacement string
• index: element in s2 where replacement comes from
• num: number of elements to use when replacing
string str = "this is an example string.";
string str3="sample phrase";
str.replace(19,6, str3, 7, 6); // "this is an example phrase."

Inserting Characters into a string
s1.insert( index, s2 ) Inserts s2 before position index
s1.insert( index, s2, index2, N );
Inserts substring of s2 before position index
Substring is N characters, starting at index2

Conversion to C-Style char*
Conversion functions
Strings are not necessarily null-terminated
s1.copy( ptr, N, index )
Copies N characters into the array ptr
Starts at location index
Need to null terminate
char str[8];
string s2 = "cathode";
s2.copy(str, 5, 2);
//copy 5 characters into str
//starting at index 2
//strcat(str,"0"); //does not work
str[5] = '0'; //this is required
cout << "str = " << str << endl;
cout << "s2 = " << s2 << endl;
Output:
str = thode
s2 = cathode

Conversion to C-Style char * Strings
Conversion functions
s1.c_str() Returns const char *
Null terminated
Example: Useful for filenames ifstream in( s1.c_str() );
s1.data() Returns const char *
NOT null-terminated

Warning!
No conversion from int or char.
The following definitions could return errors, or warnings
only, but then would cause the program to crash afterwards
string error1 = 'c’;
string error2( 'u’ );
string error3 = 22;
string error4( 8 );
However, it can be assigned one char after its declaration:
s = 'n';

C Strings oops with c++ ppt or pdf can be done.pdf

More Related Content

Similar to C Strings oops with c++ ppt or pdf can be done.pdf (20)

Recently uploaded (20)

C Strings oops with c++ ppt or pdf can be done.pdf