c ++ format inputs and outputs of the manipulator

C ++ formatted input and output

1, the format defined in the class ios control flag

ios class defines a data member: format control word flag, long x_flags

X_flags state value of each bit is defined symbolic constant enumeration: common few are listed below

enum{

skipws // skip to enter a space (skip whitespace)

left // output left-justified adjustment

right justified right // output adjustment

dec // converted to decimal (in / out) (decimalism)

oct // converted to octal (in / out) (octonary number system)

hex // converted to hexadecimal (in / out) (hexadecimal)

// display showbase all output base values, octal front plus is 0, Hex is applied in front 0x: example: dec: 255, cot: 0377, hex: 0xff

showpoint decimal point and the extra zero as // print, even if not needed

uppercase // uppercase hexadecimal output

showpos // positive integer display front plus "+" (show positive sign)

scientific // scientific notation shown float

fixed // float, and wears scientific notation corresponding to the counting method using a normal display

}；

2, the operator

Operator: two categories

Without parameters: the definition in the header file iostream.h

Parameters: the definition in the header file iomanip.h

(1) in iostream.h operator (for example the variable representing num)

oct // cout << oct << num; octal

　　　　cin>>oct<<num;

dec // cout << dec << num; Decimal

　　　　cin>>dec>>num;

hex // cout << hex << num; hexadecimal

ws // cin >> ws; // skip any leading whitespace characters (whitespace)

endl // cout << endl inserts a line break and refresh the stream

ends // cout << ends, the output of the null character '\ 0'

flush // cout << flush to empty flow

 (2)iomanip.h

setprecision (int) // set the numerical precision (rounded) cout << setprecision (5) << num;

setw (int) // set the field width cout << setw (4) << num ;

setifosflags (long p) // Enable designated as p flag cout << setifosflags (ios :: left | ios :: dec) // Left decimal output

resettifosflags (long p) // Cancel designated as a symbol of p

other

precision () Returns the current floating-point precision value

Precision (val) set to the new val precision floating-point values, and return to the original value

setf (flags) add formatting flag flags, flags of all return the original state

flags (long p) // Enable designated as a sign of p

Example:

flags()

 

int inum=255;
    cout<<"十进制方式"<<inum<<"\t";
    cout.flags(ios::oct|ios::showbase);
    cout<<"八进制方式"<<inum<<"\t";
    cout.flags(ios::hex|ios::showbase);
    cout<<"十六进制方式"<<inum<<endl;

 

　　precison()

void fn (float interest,float amount)
{
    cout<<"RMB amount=";
    cout.precision(2);
    cout<<amount<<endl;
    cout<<"\nthe interest=";
    cout.precision(4);
    cout<<interest<<endl;
}

int main ()
{
    float f1=29.41560067;
    float f2=12.567188;
    fn(f1,f2);
    return 0;
}