# Stream manipulators
Manipulators are special helper functions that help controlling input and output streams using operator >> or operator <<.
They all can be included by #include <iomanip>.
# Stream manipulators
std::boolalpha (opens new window) and std::noboolalpha (opens new window) - switch between textual and numeric representation of booleans.
std::cout << std::boolalpha << 1;
// Output: true
std::cout << std::noboolalpha << false;
// Output: 0
bool boolValue;
std::cin >> std::boolalpha >> boolValue;
std::cout << "Value \"" << std::boolalpha << boolValue
<< "\" was parsed as " << std::noboolalpha << boolValue;
// Input: true
// Output: Value "true" was parsed as 0
std::showbase (opens new window) and std::noshowbase (opens new window) - control whether prefix indicating numeric base is used.
std::dec (opens new window) (decimal), std::hex (opens new window) (hexadecimal) and std::oct (opens new window) (octal) - are used for changing base for integers.
#include <sstream>
std::cout << std::dec << 29 << ' - '
<< std::hex << 29 << ' - '
<< std::showbase << std::oct << 29 << ' - '
<< std::noshowbase << 29 '\n';
int number;
std::istringstream("3B") >> std::hex >> number;
std::cout << std::dec << 10;
// Output: 22 - 1D - 35 - 035
// 59
Default values are std::ios_base::noshowbase (opens new window) and std::ios_base::dec (opens new window).
If you want to see more about std::istringstream check out the <sstream (opens new window)> header.
std::uppercase (opens new window) and std::nouppercase (opens new window) - control whether uppercase characters are used in floating-point and hexadecimal integer output. Have no effect on input streams.
std::cout << std::hex << std::showbase
<< "0x2a with nouppercase: " << std::nouppercase << 0x2a << '\n'
<< "1e-10 with uppercase: " << std::uppercase << 1e-10 << '\n'
}
// Output: 0x2a with nouppercase: 0x2a
// 1e-10 with uppercase: 1E-10
Default is std::nouppercase.
std::setw(n) (opens new window) - changes the width of the next input/output field to exactly n.
The width property n is resetting to 0 when some functions are called (full list is here (opens new window)).
std::cout << "no setw:" << 51 << '\n'
<< "setw(7): " << std::setw(7) << 51 << '\n'
<< "setw(7), more output: " << 13
<< std::setw(7) << std::setfill('*') << 67 << ' ' << 94 << '\n';
char* input = "Hello, world!";
char arr[10];
std::cin >> std::setw(6) >> arr;
std::cout << "Input from \"Hello, world!\" with setw(6) gave \"" << arr << "\"\n";
// Output: 51
// setw(7): 51
// setw(7), more output: 13*****67 94
// Input: Hello, world!
// Output: Input from "Hello, world!" with setw(6) gave "Hello"
Default is std::setw(0).
std::left (opens new window), std::right (opens new window) and std::internal (opens new window) - modify the default position of the fill characters by setting std::ios_base::adjustfield (opens new window) to std::ios_base::left (opens new window), std::ios_base::right (opens new window) and std::ios_base::internal (opens new window) correspondingly. std::left and std::right apply to any output, std::internal - for integer, floating-point and monetary output. Have no effect on input streams.
#include <locale>
...
std::cout.imbue(std::locale("en_US.utf8"));
std::cout << std::left << std::showbase << std::setfill('*')
<< "flt: " << std::setw(15) << -9.87 << '\n'
<< "hex: " << std::setw(15) << 41 << '\n'
<< " $: " << std::setw(15) << std::put_money(367, false) << '\n'
<< "usd: " << std::setw(15) << std::put_money(367, true) << '\n'
<< "usd: " << std::setw(15)
<< std::setfill(' ') << std::put_money(367, false) << '\n';
// Output:
// flt: -9.87**********
// hex: 41*************
// $: $3.67**********
// usd: USD *3.67******
// usd: $3.67
std::cout << std::internal << std::showbase << std::setfill('*')
<< "flt: " << std::setw(15) << -9.87 << '\n'
<< "hex: " << std::setw(15) << 41 << '\n'
<< " $: " << std::setw(15) << std::put_money(367, false) << '\n'
<< "usd: " << std::setw(15) << std::put_money(367, true) << '\n'
<< "usd: " << std::setw(15)
<< std::setfill(' ') << std::put_money(367, true) << '\n';
// Output:
// flt: -**********9.87
// hex: *************41
// $: $3.67**********
// usd: USD *******3.67
// usd: USD 3.67
std::cout << std::right << std::showbase << std::setfill('*')
<< "flt: " << std::setw(15) << -9.87 << '\n'
<< "hex: " << std::setw(15) << 41 << '\n'
<< " $: " << std::setw(15) << std::put_money(367, false) << '\n'
<< "usd: " << std::setw(15) << std::put_money(367, true) << '\n'
<< "usd: " << std::setw(15)
<< std::setfill(' ') << std::put_money(367, true) << '\n';
// Output:
// flt: **********-9.87
// hex: *************41
// $: **********$3.67
// usd: ******USD *3.67
// usd: USD 3.67
Default is std::left.
std::fixed (opens new window), std::scientific (opens new window), std::hexfloat (opens new window) [C++11] and std::defaultfloat (opens new window) [C++11] - change formatting for floating-point input/output.
std::fixed sets the std::ios_base::floatfield (opens new window) to std::ios_base::fixed (opens new window),
std::scientific - to std::ios_base::scientific (opens new window),
std::hexfloat - to std::ios_base::fixed | std::ios_base::scientific and
std::defaultfloat - to std::ios_base::fmtflags(0).
fmtflags (opens new window)
#include <sstream>
...
std::cout << '\n'
<< "The number 0.07 in fixed: " << std::fixed << 0.01 << '\n'
<< "The number 0.07 in scientific: " << std::scientific << 0.01 << '\n'
<< "The number 0.07 in hexfloat: " << std::hexfloat << 0.01 << '\n'
<< "The number 0.07 in default: " << std::defaultfloat << 0.01 << '\n';
double f;
std::istringstream is("0x1P-1022");
double f = std::strtod(is.str().c_str(), NULL);
std::cout << "Parsing 0x1P-1022 as hex gives " << f << '\n';
// Output:
// The number 0.01 in fixed: 0.070000
// The number 0.01 in scientific: 7.000000e-02
// The number 0.01 in hexfloat: 0x1.1eb851eb851ecp-4
// The number 0.01 in default: 0.07
// Parsing 0x1P-1022 as hex gives 2.22507e-308
Default is std::ios_base::fmtflags(0).
There is a bug on some compilers which causes
double f;
std::istringstream("0x1P-1022") >> std::hexfloat >> f;
std::cout << "Parsing 0x1P-1022 as hex gives " << f << '\n';
// Output: Parsing 0x1P-1022 as hex gives 0
std::showpoint (opens new window) and std::noshowpoint (opens new window) - control whether decimal point is always included in floating-point representation. Have no effect on input streams.
std::cout << "7.0 with showpoint: " << std::showpoint << 7.0 << '\n'
<< "7.0 with noshowpoint: " << std::noshowpoint << 7.0 << '\n';
// Output: 1.0 with showpoint: 7.00000
// 1.0 with noshowpoint: 7
Default is std::showpoint.
std::showpos (opens new window) and std::noshowpos (opens new window) - control displaying of the + sign in non-negative output. Have no effect on input streams.
std::cout << "With showpos: " << std::showpos
<< 0 << ' ' << -2.718 << ' ' << 17 << '\n'
<< "Without showpos: " << std::noshowpos
<< 0 << ' ' << -2.718 << ' ' << 17 << '\n';
// Output: With showpos: +0 -2.718 +17
// Without showpos: 0 -2.718 17
Default if std::noshowpos.
std::unitbuf (opens new window), std::nounitbuf (opens new window) - control flushing output stream after every operation. Have no effect on input stream. std::unitbuf causes flushing.
std::setbase(base) (opens new window) - sets the numeric base of the stream.
std::setbase(8) equals to setting std::ios_base::basefield to std::ios_base::oct,
std::setbase(16) - to std::ios_base::hex,
std::setbase(10) - to std::ios_base::dec.
If base is other then 8, 10 or 16 then std::ios_base::basefield is setting to std::ios_base::fmtflags(0). It means decimal output and prefix-dependent input.
As default std::ios_base::basefield is std::ios_base::dec then by default std::setbase(10).
std::setprecision(n) (opens new window) - changes floating-point precision.
#include <cmath>
#include <limits>
...
typedef std::numeric_limits<long double> ld;
const long double pi = std::acos(-1.L);
std::cout << '\n'
<< "default precision (6): pi: " << pi << '\n'
<< " 10pi: " << 10 * pi << '\n'
<< "std::setprecision(4): 10pi: " << std::setprecision(4) << 10 * pi << '\n'
<< " 10000pi: " << 10000 * pi << '\n'
<< "std::fixed: 10000pi: " << std::fixed << 10000 * pi << std::defaultfloat << '\n'
<< "std::setprecision(10): pi: " << std::setprecision(10) << pi << '\n'
<< "max-1 radix precicion: pi: " << std::setprecision(ld::digits - 1) << pi << '\n'
<< "max+1 radix precision: pi: " << std::setprecision(ld::digits + 1) << pi << '\n'
<< "significant digits prec: pi: " << std::setprecision(ld::digits10) << pi << '\n';
// Output:
// default precision (6): pi: 3.14159
// 10pi: 31.4159
// std::setprecision(4): 10pi: 31.42
// 10000pi: 3.142e+04
// std::fixed: 10000pi: 31415.9265
// std::setprecision(10): pi: 3.141592654
// max-1 radix precicion: pi: 3.14159265358979323851280895940618620443274267017841339111328125
// max+1 radix precision: pi: 3.14159265358979323851280895940618620443274267017841339111328125
// significant digits prec: pi: 3.14159265358979324
Default is std::setprecision(6).
std::setiosflags(mask) (opens new window) and std::resetiosflags(mask) (opens new window) - set and clear flags specified in mask of std::ios_base::fmtflags type.
#include <sstream>
...
std::istringstream in("10 010 10 010 10 010");
int num1, num2;
in >> std::oct >> num1 >> num2;
std::cout << "Parsing \"10 010\" with std::oct gives: " << num1 << ' ' << num2 << '\n';
// Output: Parsing "10 010" with std::oct gives: 8 8
in >> std::dec >> num1 >> num2;
std::cout << "Parsing \"10 010\" with std::dec gives: " << num1 << ' ' << num2 << '\n';
// Output: Parsing "10 010" with std::oct gives: 10 10
in >> std::resetiosflags(std::ios_base::basefield) >> num1 >> num2;
std::cout << "Parsing \"10 010\" with autodetect gives: " << num1 << ' ' << num2 << '\n';
// Parsing "10 010" with autodetect gives: 10 8
std::cout << std::setiosflags(std::ios_base::hex |
std::ios_base::uppercase |
std::ios_base::showbase) << 42 << '\n';
// Output: OX2A
std::skipws (opens new window) and std::noskipws (opens new window) - control skipping of leading whitespace by the formatted input functions. Have no effect on output streams.
#include <sstream>
...
char c1, c2, c3;
std::istringstream("a b c") >> c1 >> c2 >> c3;
std::cout << "Default behavior: c1 = " << c1 << " c2 = " << c2 << " c3 = " << c3 << '\n';
std::istringstream("a b c") >> std::noskipws >> c1 >> c2 >> c3;
std::cout << "noskipws behavior: c1 = " << c1 << " c2 = " << c2 << " c3 = " << c3 << '\n';
// Output: Default behavior: c1 = a c2 = b c3 = c
// noskipws behavior: c1 = a c2 = c3 = b
Default is std::ios_base::skipws (opens new window).
std::quoted(s[, delim[, escape]]) (opens new window) [C++14] - inserts or extracts quoted strings with embedded spaces.
s - the string to insert or extract.
delim - the character to use as the delimiter, " by default.
escape - the character to use as the escape character, \ by default.
#include <sstream>
...
std::stringstream ss;
std::string in = "String with spaces, and embedded \"quotes\" too";
std::string out;
ss << std::quoted(in);
std::cout << "read in [" << in << "]\n"
<< "stored as [" << ss.str() << "]\n";
ss >> std::quoted(out);
std::cout << "written out [" << out << "]\n";
// Output:
// read in [String with spaces, and embedded "quotes" too]
// stored as ["String with spaces, and embedded \"quotes\" too"]
// written out [String with spaces, and embedded "quotes" too]
For more information see the link above.
# Output stream manipulators
std::ends (opens new window) - inserts a null character '\0' to output stream.
More formally this manipulator's declaration looks like
template <class charT, class traits>
std::basic_ostream<charT, traits>& ends(std::basic_ostream<charT, traits>& os);
and this manipulator places character by calling os.put(charT()) when used in an expressionos << std::ends;
std::endl (opens new window) and std::flush (opens new window) both flush output stream out by calling out.flush(). It causes immediately producing output. But std::endl inserts end of line '\n' symbol before flushing.
std::cout << "First line." << std::endl << "Second line. " << std::flush
<< "Still second line.";
// Output: First line.
// Second line. Still second line.
std::setfill(c) (opens new window) - changes the fill character to c. Often used with std::setw.
std::cout << "\nDefault fill: " << std::setw(10) << 79 << '\n'
<< "setfill('#'): " << std::setfill('#')
<< std::setw(10) << 42 << '\n';
// Output:
// Default fill: 79
// setfill('#'): ########79
std::put_money(mon[, intl]) (opens new window) [C++11]. In an expression out << std::put_money(mon, intl), converts the monetary value mon (of long double or std::basic_string type) to its character representation as specified by the std::money_put (opens new window) facet of the locale currently imbued in out. Use international currency strings if intl is true, use currency symbols otherwise.
long double money = 123.45;
// or std::string money = "123.45";
std::cout.imbue(std::locale("en_US.utf8"));
std::cout << std::showbase << "en_US: " << std::put_money(money)
<< " or " << std::put_money(money, true) << '\n';
// Output: en_US: $1.23 or USD 1.23
std::cout.imbue(std::locale("ru_RU.utf8"));
std::cout << "ru_RU: " << std::put_money(money)
<< " or " << std::put_money(money, true) << '\n';
// Output: ru_RU: 1.23 руб or 1.23 RUB
std::cout.imbue(std::locale("ja_JP.utf8"));
std::cout << "ja_JP: " << std::put_money(money)
<< " or " << std::put_money(money, true) << '\n';
// Output: ja_JP: ￥123 or JPY 123
std::put_time(tmb, fmt) (opens new window) [C++11] - formats and outputs a date/time value to std::tm according to the specified format fmt.
tmb - pointer to the calendar time structure const std::tm* as obtained from localtime() or gmtime().
fmt - pointer to a null-terminated string const CharT* specifying the format of conversion.
#include <ctime>
...
std::time_t t = std::time(nullptr);
std::tm tm = *std::localtime(&t);
std::cout.imbue(std::locale("ru_RU.utf8"));
std::cout << "\nru_RU: " << std::put_time(&tm, "%c %Z") << '\n';
// Possible output:
// ru_RU: Вт 04 июл 2017 15:08:35 UTC
For more information see the link above.
# Input stream manipulators
std::ws (opens new window) - consumes leading whitespaces in input stream. It different from std::skipws.
#include <sstream>
...
std::string str;
std::istringstream(" \v\n\r\t Wow!There is no whitespaces!") >> std::ws >> str;
std::cout << str;
// Output: Wow!There is no whitespaces!
std::get_money(mon[, intl]) (opens new window) [C++11]. In an expression in >> std::get_money(mon, intl) parses the character input as a monetary value, as specified by the std::money_get (opens new window) facet of the locale currently imbued in in, and stores the value in mon (of long double or std::basic_string type). Manipulator expects required international currency strings if intl is true, expects optional currency symbols otherwise.
#include <sstream>
#include <locale>
...
std::istringstream in("$1,234.56 2.22 USD 3.33");
long double v1, v2;
std::string v3;
in.imbue(std::locale("en_US.UTF-8"));
in >> std::get_money(v1) >> std::get_money(v2) >> std::get_money(v3, true);
if (in) {
std::cout << std::quoted(in.str()) << " parsed as: "
<< v1 << ", " << v2 << ", " << v3 << '\n';
}
// Output:
// "$1,234.56 2.22 USD 3.33" parsed as: 123456, 222, 333
std::get_time(tmb, fmt) (opens new window) [C++11] - parses a date/time value stored in tmb of specified format fmt.
tmb - valid pointer to the const std::tm* object where the result will be stored.
fmt - pointer to a null-terminated string const CharT* specifying the conversion format.
#include <sstream>
#include <locale>
...
std::tm t = {};
std::istringstream ss("2011-Februar-18 23:12:34");
ss.imbue(std::locale("de_DE.utf-8"));
ss >> std::get_time(&t, "%Y-%b-%d %H:%M:%S");
if (ss.fail()) {
std::cout << "Parse failed\n";
}
else {
std::cout << std::put_time(&t, "%c") << '\n';
}
// Possible output:
// Sun Feb 18 23:12:34 2011
For more information see the link above.
# Remarks
Manipulators can be used in other way. For example:
`is.width(n);` equals to `is >> std::setw(n);`
`is.precision(n);` equals to `is >> std::setprecision(n);`
os.setfill(c);equals toos << std::setfill(c);
str.setf(base == 8 ? std::ios_base::oct :
base == 10 ? std::ios_base::dec :
base == 16 ? std::ios_base::hex :
std::ios_base::fmtflags(0),
std::ios_base::basefield);
`is.setf(std::ios_base::flag);` equals to `is >> std::flag;`
`os.unsetf(std::ios_base::flag);` equals to `os << std::no ## flag;`
`is.unsetf(std::ios_base::flag);` equals to `is >> std::no ## flag;`
(where **##** - is **concatenation operator**)
for next `flag`s: **`boolalpha`**, **`showbase`**, **`showpoint`**, **`showpos`**, **`skipws`**, **`uppercase`**.
For `flag`s: **`dec`**, **`hex`** and **`oct`**:
`is.setf(std::ios_base::flag, std::ios_base::basefield);` equals to `is >> std::flag;`
**( 1 )**
**( 2 )**
For `flag`s: **`left`**, **`right`** and **`internal`**:
`is.setf(std::ios_base::flag, std::ios_base::adjustfield);` equals to `is >> std::flag;`
**( 1 )**
**( 2 )**
( 1 ) If flag of corresponding field previously set have already unset by unsetf.
( 2 ) If flag is set.
std::ios_base::floatfield.
`is.setf(std::ios_base::flag, std::ios_base::floatfield);` equals to `is >> std::flag;`
for `flag`s: **`fixed`** and **`scientific`**.
`is.setf(std::ios_base::fmtflags(0), std::ios_base::floatfield);` equals to `is >> std::defaultfloat;`
for `flag`s: **`basefield`**, **`adjustfield`**, **`floatfield`**.
`is.setf(mask)` equals to `is >> setiosflags(mask);`
`os.unsetf(mask)` equals to `os << resetiosflags(mask);`
`is.unsetf(mask)` equals to `is >> resetiosflags(mask);`
For almost all `mask` of `std::ios_base::fmtflags` type.