13.3 Stream Output

Formatted and unformatted output capabilities are provided by ostream. Capabilities include output of standard data types with the stream insertion operator (<<); output of characters via the put member function; unformatted output via the write member function; output of integers in decimal, octal and hexadecimal formats; output of floating-point values with various precision, with forced decimal points, in scientific notation (e.g., 1.234567e-03) and in fixed notation (e.g., 0.00123457); output of data justified in fields of designated widths; output of data in fields padded with specified characters; and output of uppercase letters in scientific notation and hexadecimal notation. We’ll demonstrate all of these capabilities in this chapter.

13.3.1 Output of char* Variables

C++ determines data types automatically—an improvement over C, but this feature sometimes “gets in the way.” For example, suppose we want to print the address stored in a char* pointer. The << operator has been overloaded to output a char* as a null-terminated C-style string. To output the address, you can cast the char* to a void* (this can be done to any pointer variable). Figure 13.1 demonstrates printing a char* variable in both string and address formats. The address prints here as a hexadecimal (base-16) number—in general, the way addresses print is implementation dependent. To learn more about hexadecimal numbers, see Appendix D, Number Systems. We say more about controlling the bases of numbers in Section 13.6.1 and Section 13.7.4.

Fig. 13.1 Printing the address stored in a char* variable.

Alternate View 

 1   // Fig. 13.1: Fig13_01.cpp
 2   // Printing the address stored in a char* variable.
 3   #include <iostream>
 4   using namespace std;
 5
 6   int main() {
 7      const char* const word{"again"};
 8
 9      // display the value of char* variable word, then display
10      // the value of word after a static_cast to void*
11      cout << "Value of word is: " << word
12         << "
Value of static_cast<const void*>(word) is: "
13         << static_cast<const void*>(word) << endl;
14   }


Value of word is: again
Value of static_cast<const void*>(word) is: 00DE8B30

13.3.2 Character Output Using Member Function put

The basic_ostream member function put outputs one character at a time. For example, the statement


cout.put('A');

displays a single character A. Calls to put may be cascaded, as in the statement


cout.put('A').put('
');

which outputs the letter A followed by a newline character. As with <<, the preceding statement executes in this manner, because the dot operator (.) associates from left to right, and the put member function returns a reference to the ostream object (cout) that received the put call. The put function also may be called with a numeric expression that represents an ASCII value, as in the following statement, which also outputs A:


cout.put(65);
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