c++ Streams

Streams

Advantages of streams

1. better type safety
2. Extensible
3. More object-oriented

Disadvantages

1. More verbose
2. Often slower
3. C标准的输入输出和C++的不能混用。

Stream naming conventions

	Input	Output	Header
Generic	istream	ostream
File	ifstream	ofstream
C string(legacy)	istrstream	ostrstream
C string	istringstream	ostringstream

Stream operations

• Extractors: Read a value from stream, overload the >> operator
• Inserters: Insert a value into a stream, overload the << operator
• Manipulators: Change the stream state

Kinds of streams

• Text streams

  Deal in ASCII text, perform some character translation, include files and character buffers

• Binary streams

  Binary data, no translations

Predefined streams

• cin: standard input
• cout: standard output
• cerr: unbuffered error(debugging) output
• clog: buffered error(debugging) output

#include 
int i;float f;char c;
char buffer[80];
//Read the next character
cin >> c;
//Read an integer
cin >> i;
//Read a float and a string separater by whitespace
cin >> f >> buffer;

More input operators

// read up to limit characters, or to delim
// Appends a null character to buf
// Does not consume the delimiter
get(char *buf, int limit, char delim = '\n')
    
// read up to limit characters, or to delim
// Appends a null character to buf
// Does consume the delimiter
getline(char *buf, int limit, char delim = '\n')
    
//Skip over limit characters or to delimiter
//Skip over delimiter if found
ignore(int limit = 1, int delim = EOF)
    
// return number of characters just read
int gcount()
cout <<"read "<

output operators

//print a single character
cout.put('a')
cerr.put('!')
    
//force output of stream contents
flush()
cout << "Enter a number"
cout.flush();

formatting using manipulators

#include

cin>>hex>>n;
cout<

manipulator	effect	type
dec, hex, oct	set numeric conversion	I,O
endl	insert newline and flush	O
flush	flush stream	O
setw(int)	set field width	I, O
setfill(ch)	change fill character	I, O
setbase(int)	set number base	O
ws	skip whitespace	I
setprecision(int)	set floating point precision	O
setiosflags(long)	turn on specified flags	I, O
resetiosflags(long)	turn off specified flags	I, O

//Working with flags
#include
#include
void main(){
    cout.setf(ios::showpos|ios::scientific);
    cout<<123<<" "<<456.78<

File streams

ifstream, ofstream connect files to streams

mode	purpose
ios::app	append
ios::ate	position at end of file
ios::binary	do binary I/O
ios::in	open for input
ios::out	open for output
ios::nocreate	don’t create file if not there
ios::noreplace	don’t replace file if present
ios::trunc	truncate file if present

# include
# include
int main(int argc, char *argv[]){
    if(argc!= 3){
        cerr<<"Usage: copy file1 file2"<< end;
        exit(1);
    }
    ifstream in(argv[1]);
    if(!in){
        cerr<< "Unable to open file"<< argv[1];
        exit(2);
    }
}

stream operations

• open(const char *, int flags, int)

  open a specified file:

  ifstream inputS;
  inputS.open("somefile", ios::in);
  if(!inputS){
      cerr<< "Unable to open somefile";
  }
  

• close()

  Close stream