Programming CC++ by conte's editor

Author:conte's editor [conte's editor]
Language: eng
Format: epub
Publisher: UNKNOWN
Published: 2020-01-18T16:00:00+00:00

int main()

{

ofstream out("test");

if(!out) {

cout << "Cannot open file.\n";

return 1;

}

// output data

out << 10 << " " << 123.23 << "\n"; out << "This is a short text file.\n"; out.close();

// now, read it back char ch;

int i;

float f;

char str[80];

ifstream in("test");

if(!in) {

cout << "Cannot open file.\n"; return 1;

}

in >> i; in >> f; in >> ch; in >> str;

cout << "Here is the data: ";

cout << i << " " << f << " " << ch << "\n"; cout << str;

in.close();

return 0; }

When reading text files using the >> operator, keep in mind that certain character translations occur. For example, whitespace characters are omitted. If you want to prevent any character translations, you must open the file for binary I/O and use the binary I/O functions.

Including ios::app causes all output to that file to be appended to the end. This value can only be used with files capable of output. Including ios::ate causes a seek to the end of the file to occur when the file is opened. Although ios::ate causes a seek to the end of file, I/O operations can still occur anywhere within the file.

The ios::binary value causes the file to be opened for binary I/O operations. By default, files are opened in text mode.

The ios::in value specifies that the file is capable of input. The ios::out value specifies that the file is capable of output. However, creating a stream using ifstream implies input, and creating a stream using ofstream implies output, so in these cases it is unnecessary to supply these values.

The ios::trunc value causes the contents of a preexisting file by the same name to be destroyed and the file is truncated to zero length.

Including ios::nocreate causes the open( ) function to fail if the file does not already exist. The ios::noreplace value causes the open( ) function to fail if the file already exists and ios::ate or ios::app is not also specified.

The value of access determines how the file can be accessed. Its default value is filebuf::openprot (filebuf is a base class of the file classes), which means a normal file. Check your compiler’s documentation for other legal values of access .

When opening a file, both mode and access will default. When opening an input file, mode will default to ios::in . When opening an output file, mode will default to ios::out. In either case, the default for access is a normal file. For example, this opens a file called “test” for output:

out.open("test"); // defaults to output and normal file

To open a stream for input and output, you must usually specify both the ios::in and the ios::out mode values, as shown here:

mystream.open("test", ios::in | ios::out);

For many compilers, no default value for mode is supplied when opening read/write files.

In all cases, if open( ) fails, the stream will be zero. Therefore, before using a file, you should test to make sure that the open operation succeeded.

Related functions are close( ) , fstream( ) , ifstream( ) , and ofstream( ) .

peek

#include <iostream.h>int peek();

The peek( ) function is a member of istream .

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