C++ Stream manipulators Stream manipulators
Example
std::boolalpha and std::noboolalpha - 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 and std::noshowbase - control whether prefix indicating numeric base is used.
std::dec (decimal), std::hex (hexadecimal) and std::oct (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 and std::ios_base::dec.
If you want to see more about std::istringstream check out the <sstream> header.
std::uppercase and std::nouppercase - 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) - 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).
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, std::right and std::internal - modify the default position of the fill characters by setting std::ios_base::adjustfield to std::ios_base::left, std::ios_base::right and std::ios_base::internal 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, std::scientific, std::hexfloat [C++11] and std::defaultfloat [C++11] - change formatting for floating-point input/output.
std::fixed sets the std::ios_base::floatfield to std::ios_base::fixed,
std::scientific - to std::ios_base::scientific,
std::hexfloat - to std::ios_base::fixed | std::ios_base::scientific and
std::defaultfloat - to std::ios_base::fmtflags(0).
fmtflags
#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 and std::noshowpoint - 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 and std::noshowpos - 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, std::nounitbuf - control flushing output stream after every operation. Have no effect on input stream. std::unitbuf causes flushing.
std::setbase(base) - 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) - 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) and std::resetiosflags(mask) - 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 and std::noskipws - 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.
std::quoted(s[, delim[, escape]]) [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.
