C++ Primer Plus

Sometimes a string may be too long to conveniently fit on one line of code. C++ enables you to concatenate string literals—that is, to combine two quoted strings into one. Indeed, any two string constants separated only by whitespace (spaces, tabs, and newlines) are automatically joined into one. Thus, all the following output statements are equivalent to each other:

cout << "I'd give my right arm to be" " a great violinist.\n";

cout << "I'd give my right arm to be a great violinist.\n";

cout << "I'd give my right ar"

"m to be a great violinist.\n";

Note that the join doesn’t add any spaces to the joined strings. The first character of the second string immediately follows the last character, not counting \0, of the first string. The \0 character from the first string is replaced by the first character of the second string.

Using Strings in an Array

The two most common ways of getting a string into an array are to initialize an array to a string constant and to read keyboard or file input into an array. Listing 4.2 demonstrates these approaches by initializing one array to a quoted string and using cin to place an input string into a second array. The program also uses the standard C library function strlen() to get the length of a string. The standard cstring header file (or string.h for older implementations) provides declarations for this and many other string-related functions.

Listing 4.2. strings.cpp

// strings.cpp -- storing strings in an array

#include

#include   // for the strlen() function

int main()

{

    using namespace std;

    const int Size = 15;

    char name1[Size];               // empty array

    char name2[Size] = "C++owboy";  // initialized array

    // NOTE: some implementations may require the static keyword

    // to initialize the array name2

    cout << "Howdy! I'm " << name2;

    cout << "! What's your name?\n";

    cin >> name1;

    cout << "Well, " << name1 << ", your name has ";

    cout << strlen(name1) << " letters and is stored\n";

    cout << "in an array of " << sizeof(name1) << " bytes.\n";

    cout << "Your initial is " << name1[0] << ".\n";

    name2[3] = '\0';                // set to null character

    cout << "Here are the first 3 characters of my name: ";

    cout << name2 << endl;

    return 0;

}

Here is a sample run of the program in Listing 4.2:

Howdy! I'm C++owboy! What's your name?

Basicman

Well, Basicman, your name has 8 letters and is stored

in an array of 15 bytes.

Your initial is B.

Here are the first 3 characters of my name: C++

Program Notes

What can you learn from Listing 4.2? First, note that the sizeof operator gives the size of the entire array, 15 bytes, but the strlen() function returns the size of the string stored in the array and not the size of the array itself. Also strlen() counts just the visible characters and not the null character. Thus, it returns a value of 8, not 9, for the length of Basicman. If cosmic is a string, the minimum array size for holding that string is strlen(cosmic) + 1.

Because name1 and name2 are arrays, you can use an index to access individual characters in the array. For example, the program uses name1[0] to find the first character in that array. Also the program sets name2[3] to the null character. That makes the string end after three characters, even though more characters remain in the array (see Figure 4.3).

Figure 4.3. Shortening a string with \0.

Note that the program in Listing 4.2 uses a symbolic constant for the array size. Often the size of an array appears in several statements in a program. Using a symbolic constant to represent the size of an array simplifies revising the program to use a different array size; you just have to change the value once, where the symbolic constant is defined.

Adventures in String Input

The strings.cpp program has a blemish that is concealed through the often useful technique of carefully selected sample input. Listing 4.3 removes the veils and shows that string input can be tricky.

Listing 4.3. instr1.cpp

// instr1.cpp -- reading more than one string

#include

int main()

{

    using namespace std;

    const int ArSize = 20;

    char name[ArSize];

    char dessert[ArSize];

    cout << "Enter your name:\n";

    cin >> name;

    cout << "Enter your favorite dessert:\n";

    cin >> dessert;

    cout << "I have some delicious " << dessert;

    cout << " for you, " << name << ".\n";

    return 0;

}

The intent of the program in Listing 4.3 is simple: Read a user’s name and favorite dessert from the keyboard and then display the information. Here is a sample run:

Enter your name:

Alistair Dreeb

Enter your favorite dessert:

I have some delicious Dreeb for you, Alistair.

We didn’t even get a chance to respond to the dessert prompt! The program showed it and then immediately moved on to display the final line.