Strings (string)

Definition

An instance s of the data type string is a sequence of characters (type char). The number of characters in the sequence is called the length of s. A string of length zero is called the empty string. Strings can be used wherever a C++char* string can be used.

Strings differ from the C++type char* in several aspects: parameter passing by value and assignment works properly (i.e., the value is passed or assigned and not a pointer to the value) and strings offer many additional operations.

Creation

string	s;	introduces a variable s of type string. s is initialized with the empty string.
string	s(const char* p);	introduces a variable s of type string. s is initialized with a copy of the C ++string p.
string	s(const char* format, ...);
		introduces a variable s of type string. s is initialized with the string produced by printf(format,...).
string	s(char c);	introduces a variable s of type string. s is initialized with the one-character string ``c''.

Operations

int	s.length()	returns the length of string s.
char&	s[int i]	returns the character at position i. Precondition: 0 <= i <= s.length()-1.
string	s(int i, int j)	returns the substring of s starting at position max(0,i) and ending at position min(j,s.length()-1). If min(j,s.length()-1) < max(0,i) then the empty string is returned.
string	s.head(int i)	returns the first i characters of s.
string	s.tail(int i)	returns the last i characters of s.
int	s.pos(string s1, int i)	returns the minimum j such that j >= i and s_1 is a substring of s starting at position j (returns -1 if no such j exists).
int	s.pos(string s1)	returns pos(s1,0).
string	s.insert(int i, string s1)
		returns s(0,i-1) + s_1 + s(i,s.length()-1).
string	s.replace(string s1, string s2, int i=1)
		returns the string created from s by replacing the i-th occurrence of s_1 in s by s_2.
string	s.replace(int i, int j, string s1)
		returns the string created from s by replacing s(i,j) by s_1. Precondition: i <=q j.
string	s.replace(int i, string s1)
		returns the string created from s by replacing s[i] by s_1.
string	s.replace_all(string s1, string s2)
		returns the string created from s by replacing all occurrences of s_1 in s by s_2. Precondition: The occurrences of s_1 in s do not overlap (it's hard to say what the function returns if the precondition is violated.).
string	s.del(string s1, int i=1)	returns s.replace(s_1,"",i).
string	s.del(int i, int j)	returns s.replace(i,j,"").
string	s.del(int i)	returns s.replace(i,"").
string	s.del_all(string s1)	returns s.replace_all(s_1,"").
void	s.read(istream& I, char delim = ' ')
		reads characters from input stream I into s until the first occurrence of character delim.
void	s.read(char delim = ' ')	same as to s.read(cin,delim).
void	s.read_line(istream& I)	same as to s.read(I,' $\backslash$ n').
void	s.read_line()	same as to s.read_line(cin).
void	s.read_file(istream& I)	same as to s.read(I,'EOF').
void	s.read_file()	same as to s.read_file(cin).
string&	s += x	appends x to s and returns a reference to s.
string	x + y	returns the concatenation of x and y.
bool	x == y	true iff x and y are equal.
bool	x != y	true iff x and y are not equal.
bool	x < y	true iff x is lexicographically smaller than y.
bool	x > y	true iff x is lexicographically greater than y.
bool	x <= y	returns (x < y) | (x == y).
bool	x >= y	returns (x > y) | (x == y).
istream&	istream& I >> string& s	same as to s.read(I,' ').
ostream&	ostream& O << s	writes string s to the output stream O.

Implementation

Strings are implemented by C++character vectors. All operations involving the search for a pattern s1 in a string s take time O(s.lenght() * s1.length()), [ ] takes constant time and all other operations on a string s take time O(s.length()).