Characters, Strings, and Cstring Library in C++
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Characters, Strings, and
the cstring Library
Andy Wang
Object Oriented Programming in C++
COP 3330
Recap
•
A C-style string is a char array that ends with the null
character
•
Character literals
are in single quotes
•
‘a’, ‘\n’, ‘$’
•
String literals
are in double quotes
•
“Hello world\n”
•
The null character is an implicit part of a string literal
Recap
•
The name of an array points to the first element of
an array
•
When an array is passed into a function, the function can
access the original array
The cctype Library
•
Conversion functions
return the ASCII value of a
character
•
int touper(int c) returns the uppercase version of c
•
int tolower(int c) returns the lowercase version of c
Query functions
•
Return true (non-zero) or false (0) to question posed
by the function’s name
•
int isdigit(int c)
•
int isalpha(int c)
•
int isalnum(int c)
// a digit or a letter
•
int islower(int c);
•
int isupper(int c);
Query functions
•
int isxdigit(int c)
// hex digit (0-9, a-f)?
•
int isspace(int c)
// white space?
•
int iscntrl(int c)
// control character?
•
int ispunct(int c)
// printing character other than space,
// letter, digit?
•
int isprint(int c)
// printing character (including ‘ ’)?
•
int isgraph(int c)
// printing other other than ‘ ‘ (space)?
String I/O
•
Insertion (<<) and extraction (>>)
char greeting[20] = “Hello, world”;
cout << greeting;
// prints “Hello, world”
char lastname[20];
cin >> lastname;
// reads a string into lastname
// adds ‘\0’ automatically
•
The insertion operator << will print the content of a
char array, up to the first null character
•
The extraction operator >> will read in a string, and
stop at a white space
String I/O
•
The cin examples reads one word at a time
•
How to read a whole sentence into a string?
Reading strings: get and getline
•
Two member functions in class istream (in the
iostream library)
char *get(char str[], int length, char delimiter = ‘\n’);
char *getline(char str[], int length, char delimiter = ‘\n’);
•
Note that the get function with only one parameter
can only read a single character from the input
stream
char ch;
ch = cin.get();
// extracts one char and returns it
cin.get(ch);
// extracts one char and stores in ch
get and getline Functions (with
Three Parameters)
•
Read and store a c-style string
•
str is the char array where the data will be stored
•
Note that it is passed by reference
•
length is the size of the array
•
delimiter (optional, with ‘\n’ as default) specifies when to
stop reading
•
Automatically appends ‘\0’
Example
•
Sample calls
char buffer[80];
cin >> buffer;
// reads one word into buffer
cin.get(buffer, 80, ‘,’);
// reads up to the first comma
cin.getline(buffer, 80);
// reads an entire line (up to endl)
•
So, what is the difference between get and getline?
•
get will leave the delimiter character on the input stream
•
getline will extract and discard the delimiter
Another Example
•
Input
Hello, world
Joe Smith. He says hello.
•
Code
char greeting[15], name[10], other[20];
cin.getline(greeting, 15);
// “Hello, world”
cin.get(name, 10, ‘.’);
// “Joe Smith”
cin.getline(other, 20);
// “. He says hello.”
Example String Calls
•
http://www.cs.fsu.edu/~myers/c++/examples/strin
gs/io1.cpp
io1.cpp
#include <iostream>
using name space std;
int main() {char string1[30], string2[30], string3[30], string4[30];
// print some instructions
cin >> string1; // get one word, append it with ‘\0’
cin.getline(string2, 30, ‘,’); // get line, drop ‘,’
cin.get(string3, 30, ‘e’); // get up to ‘e’
cin.get(string4, 30); // get 30 chars
io1.cpp
cout << “\n\nOutputs:\n”;
cout << “string1 = “ << string1 << endl;
cout << “string2 = “ << string2 << endl;
cout << “string3 = “ << string3 << endl;
cout << “string4 = “ << string4 << endl;
return 0;
}
Program Execution
> To be, or not to be, that is the question.
Program Execution
> To be, or not to be, that is the question.
Outputs:
string1 = To
string2 = be
string3 = or not to b
string4 = e, that is the question.
Standard C String Library
•
To use it, #include <cstring>
•
int strlen(const char str[]);
•
Takes a string argument, returns its length (excluding ‘\0’)
•
Sample calls
char phrase[30] = “Hello, world”;
cout << strlen(“Greetings, Earthling!”); // prints 21
int length = strlen(phrase);
// stores 12
strcpy
•
char *strcpy(char str1[], const char str2[]);
•
Takes two string arguments, and copies the contents of the
second string into the first string
•
Sample calls
char buffer[80], firstname[30], lastname[30] = “Smith”;
strcpy(firstname, “Billy Joe Bob”);
strcpy(buffer, lastname);
cout << firstname; // prints “Billy Joe Bob”
cout << buffer;
// prints “Smith”
strcat
•
char *strcat(char str1[], const char str2[]);
•
Takes two string arguments, and concatenates the second
one onto the first
•
Sample calls
char buffer[80] = “Dog”;
char word[] = “food”;
strcat(buffer, word);
// buffer is now Dogfood
strcat(buffer, “ breath”);
// buffer is now Dogfood breath
strcmp
•
int strcmp(const char str1[], const char str2[]);
•
Takes two string arguments
•
Returns 0 if they are equal
•
Returns a negative number if str1 comes before str2 (based
on ASCII code)
•
Returns a positive number if str2 comes before str1
strcmp Sample Calls
char word1[30] = “apple”;
char word2[30] = “apply”;
if (strcmp(word1, word2) != 0)
cout << “The words are different\n”;
strcmp(word1, word2); // < 0, word1 comes first
strcmp(word1, “apple”); // 0, words are the same
strcmp(“apple”, “Zebra”); // > 0, uppercase first
strcmp
•
Note strcmp relies on ‘\0’ at the end of each string
•
No built-in bound checking in C++
strncpy, strncat, strncmp
•
Same as strcpy, strcat, strcmp
•
Takes an additional integer N as an argument
•
Processes up to ‘\0’ or N characters
strncpy, strncat, strncmp
•
Examples
char buffer[80];
char word[11] = “applesause”;
char bigword[] = “supercalifragilisticexpialidocious”;
strncpy(buffer, word, 5); // buffer = “apple”
strncat(buffer, “ piecemeal”, 4); // buffer = “apple pie”
strncmp(buffer, “apple”, 5); // returns 0
strncpy(word, bigword, 10); // word = “supercalif”
This content delves into the usage of characters, strings, and the cstring library in C++. Covering topics such as C-style strings, character literals, array functions, conversion functions, query functions, string I/O operations, and more, it provides a comprehensive overview essential for mastering object-oriented programming in C++.
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Presentation Transcript
Characters, Strings, and the cstring Library Andy Wang Object Oriented Programming in C++ COP 3330
Recap A C-style string is a char array that ends with the null character Character literals are in single quotes a , \n , $ String literals are in double quotes Hello world\n The null character is an implicit part of a string literal
Recap The name of an array points to the first element of an array When an array is passed into a function, the function can access the original array
The cctype Library Conversion functions return the ASCII value of a character int touper(int c) returns the uppercase version of c int tolower(int c) returns the lowercase version of c
Query functions Return true (non-zero) or false (0) to question posed by the function s name int isdigit(int c) int isalpha(int c) int isalnum(int c) // a digit or a letter int islower(int c); int isupper(int c);
Query functions int isxdigit(int c) int isspace(int c) int iscntrl(int c) int ispunct(int c) // hex digit (0-9, a-f)? // white space? // control character? // printing character other than space, // letter, digit? int isprint(int c) int isgraph(int c) // printing character (including )? // printing other other than (space)?
String I/O Insertion (<<) and extraction (>>) char greeting[20] = Hello, world ; cout << greeting; char lastname[20]; cin >> lastname; // prints Hello, world // reads a string into lastname // adds \0 automatically The insertion operator << will print the content of a char array, up to the first null character The extraction operator >> will read in a string, and stop at a white space
String I/O The cin examples reads one word at a time How to read a whole sentence into a string?
Reading strings: get and getline Two member functions in class istream (in the iostream library) char *get(char str[], int length, char delimiter = \n ); char *getline(char str[], int length, char delimiter = \n ); Note that the get function with only one parameter can only read a single character from the input stream char ch; ch = cin.get(); // extracts one char and returns it cin.get(ch); // extracts one char and stores in ch
get and getline Functions (with Three Parameters) Read and store a c-style string str is the char array where the data will be stored Note that it is passed by reference length is the size of the array delimiter (optional, with \n as default) specifies when to stop reading Automatically appends \0
Example Sample calls char buffer[80]; cin >> buffer; cin.get(buffer, 80, , ); // reads up to the first comma cin.getline(buffer, 80); // reads an entire line (up to endl) So, what is the difference between get and getline? get will leave the delimiter character on the input stream getline will extract and discard the delimiter // reads one word into buffer
Another Example Input Hello, world Joe Smith. He says hello. Code char greeting[15], name[10], other[20]; cin.getline(greeting, 15); cin.get(name, 10, . ); cin.getline(other, 20); // Hello, world // Joe Smith // . He says hello.
Example String Calls http://www.cs.fsu.edu/~myers/c++/examples/strin gs/io1.cpp
io1.cpp #include <iostream> using name space std; int main() { char string1[30], string2[30], string3[30], string4[30]; // print some instructions cin >> string1; // get one word, append it with \0 cin.getline(string2, 30, , ); // get line, drop , cin.get(string3, 30, e ); // get up to e cin.get(string4, 30); // get 30 chars
io1.cpp cout << \n\nOutputs:\n ; cout << string1 = << string1 << endl; cout << string2 = << string2 << endl; cout << string3 = << string3 << endl; cout << string4 = << string4 << endl; return 0; }
Program Execution > To be, or not to be, that is the question.
Program Execution > To be, or not to be, that is the question. Outputs: string1 = To string2 = be string3 = or not to b string4 = e, that is the question.
Standard C String Library To use it, #include <cstring> int strlen(const char str[]); Takes a string argument, returns its length (excluding \0 ) Sample calls char phrase[30] = Hello, world ; cout << strlen( Greetings, Earthling! ); // prints 21 int length = strlen(phrase); // stores 12
strcpy char *strcpy(char str1[], const char str2[]); Takes two string arguments, and copies the contents of the second string into the first string Sample calls char buffer[80], firstname[30], lastname[30] = Smith ; strcpy(firstname, Billy Joe Bob ); strcpy(buffer, lastname); cout << firstname; // prints Billy Joe Bob cout << buffer; // prints Smith
strcat char *strcat(char str1[], const char str2[]); Takes two string arguments, and concatenates the second one onto the first Sample calls char buffer[80] = Dog ; char word[] = food ; strcat(buffer, word); strcat(buffer, breath ); // buffer is now Dogfood breath // buffer is now Dogfood
strcmp int strcmp(const char str1[], const char str2[]); Takes two string arguments Returns 0 if they are equal Returns a negative number if str1 comes before str2 (based on ASCII code) Returns a positive number if str2 comes before str1
strcmp Sample Calls char word1[30] = apple ; char word2[30] = apply ; if (strcmp(word1, word2) != 0) cout << The words are different\n ; strcmp(word1, word2); // < 0, word1 comes first strcmp(word1, apple ); // 0, words are the same strcmp( apple , Zebra ); // > 0, uppercase first
strcmp Note strcmp relies on \0 at the end of each string No built-in bound checking in C++
strncpy, strncat, strncmp Same as strcpy, strcat, strcmp Takes an additional integer N as an argument Processes up to \0 or N characters
strncpy, strncat, strncmp Examples char buffer[80]; char word[11] = applesause ; char bigword[] = supercalifragilisticexpialidocious ; strncpy(buffer, word, 5); // buffer = apple strncat(buffer, piecemeal , 4); // buffer = apple pie strncmp(buffer, apple , 5); // returns 0 strncpy(word, bigword, 10); // word = supercalif
