关于输出
c++中的cout和c中printf输出同样东西的时候
为什么结果有时候不同呢
他们哪里有区别呢，谢谢
问题点数：0、回复次数：10Top
1 楼kobefly（科比--网络学习中）回复于 2005-04-04 18:10:22 得分 0
cout比printf智能啊Top
2 楼solid123（游戏机）回复于 2005-04-04 18:27:44 得分 0
cout比printf少2个字母啊~~~Top
3 楼leon8341（Leon）回复于 2005-04-04 18:59:08 得分 0
cout简单啊，不用输入格式化字符Top
4 楼pcboyxhy（-273.15℃）回复于 2005-04-04 19:03:29 得分 0
cout速度慢Top
5 楼yangkun110（狼的传人）回复于 2005-04-04 19:03:57 得分 0
COUT 叼Top
6 楼yangkun110（狼的传人）回复于 2005-04-04 19:04:28 得分 0
给分就是了， 管他多哦Top
7 楼style1984（）回复于 2005-04-04 19:13:43 得分 0
如果用cout在输出字符串时，你就可以看出它的优越老！！！Top
8 楼xiaozhishi（彭志）回复于 2005-04-04 19:21:59 得分 0
你知道吗
知道就告诉我哦
我不知道呢Top
9 楼xjp6688（大平/要做必须最好）回复于 2005-04-05 08:59:32 得分 0
Summary
Controls output to a stream buffer associated with the object stdout declared in <cstdio>.
Synopsis
#include <iostream>
extern ostream cout;
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.
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 Puts 揬n?and flush
ends Puts 揬0?and flush
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抯 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 with (number of characters) to generate on certain output conversions
endl Inserts a newline character into the output sequence and flush the output buffer.
ends Inserts a null character into the output sequence.
flush Flush the output buffer.
Default Values
precision() 6
width() 0
fill() the space character
flags() skipws | dec
getloc() locale::locale()
Example
//
// cout example #1
//
#include<iostream>
#include<iomanip>
void main ( )
{
using namespace std;
int i;
float f;
// read an integer and a float from stdin
cin >> i >> f;
// output the integer and goes at the line
cout << i << endl;
// output the float and goes at the line
cout << f << endl;
// output i in hexa
cout << hex << i << endl;
// output i in octal and then in decimal
cout << oct << i << dec << i << endl;
// output i preceded by its sign
cout << showpos << i << endl;
// output i in hexa
cout << setbase(16) << i << endl;
// output i in dec and pad to the left with character
// @ until a width of 20
// if you input 45 it outputs 45@@@@@@@@@@@@@@@@@@
cout << setfill('@') << setw(20) << left << dec << i;
cout << endl;
// output the same result as the code just above
// but uses member functions rather than manipulators
cout.fill('@');
cout.width(20);
cout.setf(ios_base::left, ios_base::adjustfield);
cout.setf(ios_base::dec, ios_base::basefield);
cout << i << endl;
// outputs f in scientific notation with
// a precision of 10 digits
cout << scientific << setprecision(10) << f << endl;
// change the precision to 6 digits
// equivalents to cout << setprecision(6);
cout.precision(6);
// output f and goes back to fixed notation
cout << f << fixed << endl;
}
//
// cout example #2
//
#include <iostream>
void main ( )
{
using namespace std;
char p[50];
cin.getline(p,50);
cout << p;
}
//
// cout example #3
//
#include <iostream>
#include <fstream>
void main ( )
{
using namespace std;
// open the file "file_name.txt"
// for reading
ifstream in("file_name.txt");
// output the all file to stdout
if ( in )
cout << in.rdbuf();
else
{
cout << "Error while opening the file";
cout << endl;
}
}
Warnings
Keep in mind that the manipulator endl flushes the stream buffer. Therefore it is recommended to use 慭n?if your only intent is to go at the line. It greatly improves performance when C and C++ streams are not synchronized.
If your compiler does not support namespaces, then you do not need the using declaration for std.
See Also
basic_ostream(3C++), basic_iostream(3C++), basic_filebuf(3C++), cin(3C++), cerr(3C++), clog(3C++), wcin(3C++), wcout(3C++), wcerr(3C++), wclog(3C++)
Working Paper for Draft Proposed International Standard for Information Systems--Programming Language C++, Section 27.3.1
Standards Conformance
ANSI X3J16/ISO WG21 Joint C++ CommitteeTop
10 楼greatjzl（）回复于 2005-04-05 09:36:13 得分 0
ftTop
