Stream manipulators:
*
Remarks
*
Stream manipulators
Stream manipulators
suggest changestd::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).
#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 << "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 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.
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:
- http://en.cppreference.com/w/cpp/io/manip/booalpha
- http://en.cppreference.com/w/cpp/io/manip/showbase
- http://en.cppreference.com/w/cpp/io/manip/hex
- http://en.cppreference.com/w/cpp/io/ios_base/fmtflags
- http://en.cppreference.com/w/cpp/io/manip/uppercase
- http://en.cppreference.com/w/cpp/io/manip/left
- http://en.cppreference.com/w/cpp/io/manip/fixed
- http://en.cppreference.com/w/cpp/io/manip/showpoint
- http://en.cppreference.com/w/cpp/io/manip/showpos
- http://en.cppreference.com/w/cpp/io/manip/unitbuf
- http://en.cppreference.com/w/cpp/io/manip/skipws
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Table Of Contents
1
Literals
8
Arrays
11
Loops
14
keywords
16
auto keyword
17
Pointers
20
std::string
21
Enumeration
22
std::atomic
23
std::vector
24
std::array
25
std::pair
26
std::map
29
std::any
30
std::variant
35
std::iomanip
36
Iterators
37
Basic I/O
38
File I/O
39
Streams
40
Stream manipulators
43
References
44
Polymorphism
51
Unions
52
Templates
53
Namespaces
56
Lambdas
57
Threading
59
Preprocessor
60
SFINAE
62
RAII
63
Exceptions
67
Sorting
74
Pimpl idiom
75
Copy elision
78
Singleton
81
Type erasure
84
RTTI
87
Scopes
88
Atomic types
90
constexpr
98
Type traits
102
Attributes
104
Profiling
107
Recursion
108
Callable objects
111
Inline functions
113
Header files
116
Parameter packs
117
Iteration
118
type deduction
120
Build systems
122
Type inference
125
Alignment
126
Inline variables
133
Optimization
134
Semaphore
136
Debugging
139
Mutexes
140
Recursive mutex
141
Unit testing
142
decltype
143
Digit separators
144
C++ Containers
146
Contributors