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This data structure is outdated.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