Apache C++ Standard Library Reference Guide

## cout

Library: Input/output

- Local Index
- Summary
- Synopsis
- Description
- Formatting
- Description
- Default Values
- Warnings
- See Also
- Standards Conformance

### Local Index

No Entries

### Summary

Predefined stream that controls output to a stream buffer associated with the object `stdout` declared in `<cstdio>`

### Synopsis

    #include <iostream>

    namespace std {
      extern ostream cout;
    }

### Description

The object `cout` controls output to a stream buffer associated with the object `stdout` declared in `<cstdio>`. By default the standard C and C++ streams are synchronized, but performance improvement can be achieved by using the ios_base member function `synch_with_stdio` to desynchronize them.

After the object `cin` is initialized, `cin.tie()` returns `&cout`, which implies that `cin` and `cout` are synchronized.

### Formatting

The formatting is done through member functions or manipulators.

#### Table 16: Formatting functions and manipulators for cout

Manipulators | Member functions
`showpos` | `setf(ios_base::showpos)`
`noshowpos` | `unsetf(ios_base::showpos)`
`showbase` | `setf(ios_base::showbase)`
`noshowbase` | `unsetf(ios_base::showbase)`
`uppercase` | `setf(ios_base::uppercase)`
`nouppercase` | `unsetf(ios_base::uppercase)`
`showpoint` | `setf(ios_base::showpoint)`
`noshowpoint` | `unsetf(ios_base::showpoint)`
`boolalpha` | `setf(ios_base::boolalpha)`
`noboolalpha` | `unsetf(ios_base::boolalpha)`
`unitbuf` | `setf(ios_base::unitbuf)`
`nounitbuf` | `unsetf(ios_base::unitbuf)`
`internal` | `setf(ios_base::internal,` `ios_base::adjustfield)`
`left` | `setf(ios_base::left,` `ios_base::adjustfield)`
`right` | `setf(ios_base::right,` `ios_base::adjustfield)`
`dec` | `setf(ios_base::dec,` `ios_base::basefield)`
`hex` | `setf(ios_base::hex,` `ios_base::basefield)`
`oct` | `setf(ios_base::oct,` `ios_base::basefield)`
`fixed` | `setf(ios_base::fixed,` `ios_base::floatfield)`
`scientific` | `setf(ios_base::scientific,` `ios_base::floatfield)`
`resetiosflags` `(ios_base::fmtflags flag)` | `setf(0,flag)`
`setiosflags` `(ios_base::fmtflags flag)` | `setf(flag)`
`setbase(int base)` | see above
`setfill(char_type c)` | `fill(c)`
`setprecision(int n)` | `precision(n)`
`setw(int n)` | `width(n)`
`endl` |
`ends` |
`flush` | `flush( )`

### Description

`showpos` | Generates a + sign in non-negative generated numeric output.
`showbase` | Generates a prefix indicating the numeric base of generated integer output
`uppercase` | Replaces certain lowercase letters with their uppercase equivalents in generated output
`showpoint` | Generates a decimal-point character unconditionally in generated floating-point output
`boolalpha` | Inserts and extracts bool type in alphabetic format
`unitbuf` | Flushes output after each output operation
`internal` | Adds fill characters at a designated internal point in certain generated output. If no such point is designated, it's identical to `right`.
`left` | Adds fill characters on the right (final positions) of certain generated output
`right` | Adds fill characters on the left (initial positions) of certain generated output
`dec` | Converts integer input or generates integer output in decimal base
`hex` | Converts integer input or generates integer output in hexadecimal base
`oct` | Converts integer input or generates integer output in octal base
`fixed` | Generates floating-point output in fixed-point notation
`scientific` | Generates floating-point output in scientific notation
`resetiosflags(ios_base::fmtflags flag)` | Resets the `fmtflags` field `flag`
`setiosflags(ios_base::fmtflags flag)` | Sets up the flag `flag`
`setbase(int base)` | Converts integer input or generates integer output in base `base`. The parameter `base` can be 8, 10 or 16.
`setfill(char_type c)` | Sets the character used to pad (fill) an output conversion to the specified field width
`setprecision(int n)` | Sets the precision (number of digits after the decimal `point) to generate on certain output conversions`
`setw(int n)` | Sets the field width (number of characters) to generate on certain output conversions
`endl` | Inserts a newline character into the output sequence and flushes the output buffer
`ends` | Inserts a null character into the output sequence
`flush` | Flushes the output buffer

### Default Values

    precision()            6
    width()                0
    fill()                 the space character
    flags()                skipws | dec
    getloc()               locale::locale()

### Warnings

Keep in mind that while the manipulator `endl` flushes the stream buffer, outputting the character `'\n'` is not guaranteed to flush the stream buffer. You should output the `'\n'` character without `endl` only if you do not need the buffer flushed. Note that outputting the `'\n'` character in such cases, and hence not forcing a buffer flush, may result in a performance improvement. It greatly improves performance when C and C++ streams are not synchronized.

### See Also

basic_ostream, basic_iostream, basic_filebuf, cin, cerr, clog, wcin, wcout, wcerr, wclog

### Standards Conformance

ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++, Section 27.3.1