Manupulating strings and arrays together in c plus plus?

Answer 1

A string is an array; an array of character data types (char or wchar_t). Therefore anything you can do with an array you can also do with a string.

C does not have a built-in type for either an array or a string, but C++ does. In C, the programmer was entirely responsible for managing the memory allocated to an array. Built-in functions allowed us to determine the length of a null-terminated string, append strings, or alter the amount of memory allocated to an array, but the functions and the arrays were entirely separate. With C++, std::vector and std::string objects allow us to manipulate dynamic arrays and variable length strings, respectively, without having to worry about the underlying memory allocations. Since all the required methods are encapsulated within the objects themselves, they are much easier to work with.

For instance, in C, if we wanted to determine the length of a string we might call the strlen function:

char* str = "Hello world!";

unsigned size = strlen (str);

Arrays are a bit more difficult in that we must maintain a separate variable to keep track of an array's length:

unsigned size = 10;

int* arr = malloc(size);

size = 11;

arr = realloc(arr, size);

In C++, strings and arrays know their own length, so we don't need to call external functions or maintain separate variables:

std::string str = "Hello world!";

std::cout << '"' << str << '"' << " has " << str.size() << " characters\n";

std::vector<int> vect(10,0);

std::cout << "vect has " << vect.size() << " elements\n";

A vector of strings allows us to manipulate strings and vectors together. A vector of strings is essentially a two-dimensional dynamic array where each row is a string, and every string can have different lengths. The following therefore creates a vector with 10 empty strings:

std::vector< std::string > vstrings (10, "");

We can then manipulate each of the individual strings in the array:

vstrings[0] = "Hello world!";

vstrings[1] = "Another string.";

vstrings[2] = "The third string.";

...

vstrings[9] = "The string to end all strings.";

Each of these strings is a different length. With a traditional two-dimensional array each row would be the same length. In this case we'd need at least a 10 x 31 array (including null-terminators), which wastes memory when any string is less than 30 characters long. The only way to resolve this is to use a one-dimensional array of pointers to strings instead. Vectors of strings do the same thing, but they are much easier to work with since all memory management is handled by the objects themselves.