.. highlight:: c++
  :linenothreshold: 5

********
C String
********
A data structure inherited from C language to handle variable-length text.

This data structure is outdated. It is hard and insecure to use. The C++ string
type is preferred.

+ A partially filed char array with a '\\0' (null) char to mark the end
+ not a class type. no methods!
+ [] syntax

  * no out-of-range check

Example
=======

* ``char str1[100] = "abc"``

  - The C string can hold up to 99 characters (not 100)
  - The string length is 3 (not include the tailing '\\0')
  - The occupied spaces is 4 (include the tailing '\\0')

* ``char str1[] = "abc"``

  - The string length is 3
  - The array length is 4 (include the tailing '\\0')
  - The array is filled

* loop through a C string::

    // scan through the C string once
    char cstr1[] = "abcde";
    for (int i = 0; cstr1[i] != '\0'; ++i)
      cout << cstr1[i];

    // strlen will scan through the array once
    // scan through the C string twice
    for (int i = 0; i < strlen(cstr1); ++i)
      cout << cstr1[i];

* dynamic C string::

    char *dyn_str1 = new char[100];
    strcpy(dyn_str1, "abc");
    delete [] dyn_str1;

Pitfalls
========

* ``cout << myString.size();`` C string has no method at all
* ``char str1[10] = {0}; cout << str1[10];`` out-of-range access
* ``char str2[3] = "abc";`` overflows, the str2 can have at most two chars

C String Related Functions
==========================
* c-string header ``#include <cstring>``
* ``strcpy`` copy
* ``strncpy`` copy with cut off
* ``strcat`` concatenate
* ``strncat`` concatenate with cut off
* ``strchar`` search a char in a C string
* ``strlen`` get length
* ``strcmp`` compare two C strings

char Functions
==============

* cctype header (not typo, two c letters) ``#include <cctype>``
* ``isalpha``
* ``isdigit``
* ``isspace``
* ``islower``
* ``isupper``
* ``toupper``
* ``tolower``