Strings

Objectives

1. 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