Strings

Objectives

We would like to :

Investigate both C and C++ strings.

Notes

A string is a collection of characters.
- In c++ string word;
In c

char word[] = "the string";

char * word = strdup("the string");

Careful here, we need to delete this memory after we are done with it.

In general a c style string is an array of characters.

But the last character is a null (0)

Manipulation of strings is most commonly done with a library function.

#include <string.h> or #include <cstring>

reference.

strdup makes a copy of a string
strcat concatenates two strings
strlen returns the length of the string.
etc.

In modern usage c style strings are discouraged.

They are a common source of buffer overflow errors
Hence a source of security problems.

But at times you will need these

If you are working in c
If you are interfacing with c style libraries
Or when you write assembly code!

C++ style strings

reference.
This is an example of a class.
- Actually a hierarchy of classes.
A class is a collection of data and the operations on that data.
The operations are called methods
The class handles the memory management.
- Direct assignment and copy
- Easy string concatenation.
There are many methods.
- Before you write a function you should check the methods
- Unless you are told not to in an assignment statement.
size_t
- reference
- This is an integer type
- It is unsigned as it is designed for use with arrays
- It is an abstraction, most likely a unsigned int or unsigned long
- It will cause some compiler errors.
- What are the rules for array indexing?
string::npos reference. This is a constant from the string library It is a size_t It is a non-existent position in a string, probably string max size + 1.
run c+string Do you really want to know either of these? Use the symbolic names Why do we declare things like this?
You should know size,length - return the number of characters in the string. [n] returns the character at a given position find(substr, startpos) - find the substring starting at position starpos Returns the starting position of the substring (>= startpos if given) Or string::npos if not present. substr(startpos, length) - extract a substring Starts at startpos If length is specified, stop there If length is not specified, go to the end of the string. sto* (stoi, stol, stoll, stof, stod, ...) to_string (int or floating point to string)

 Some helpful character functions
    
         reference.
        
 From #incldue <cctype> , 
        
 is*
        
 to*
        
 All take an int and return an int.
        
 But they are really character.

 >>, and getline with strings

 A word of caution
    
         Linux terminates lines in a file with \n
        
 Windows terminates lines in a file with \r\n
        
 c/c++ only expects \n
        
 dos2unix and unix2dos