C++ Tutorial/File Stream/ifstream
Содержание
- 1 Display a file from a given starting point
- 2 Display a file using ifstream.get()
- 3 ifstream: read buffer and seek file position
- 4 Ignore up to 10 characters or until first space is found
- 5 Read and display a text file line by line.
- 6 12. 8. 5. Reading a text file
- 7 Reading numbers from a file
- 8 Show a file from starting offset
- 9 Use ifstream.read() and ofstream.write()
Display a file from a given starting point
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
int main(int argc, char *argv[])
{
char ch;
ifstream in("test.txt", ios::in | ios::binary);
if(!in) {
cout << "Cannot open file.\n";
return 1;
}
in.seekg(1, ios::beg);
while(in.get(ch))
cout << ch;
return 0;
}0 123.23 This is a text.
Display a file using ifstream.get()
#include <iostream>
#include <fstream>
using namespace std;
int main(int argc, char *argv[])
{
char ch;
ifstream in("test", ios::in | ios::binary);
if(!in) {
cout << "Cannot open file.\n";
return 1;
}
while(in) { // in will be false when eof is reached
in.get(ch);
if(in) cout << ch;
}
in.close();
return 0;
}hello
ifstream: read buffer and seek file position
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
// header files for file I/O
#include <iostream>
#include <fstream>
void printFileTwice (const char* filename)
{
// open file
std::ifstream file(filename);
// print contents the first time
std::cout << file.rdbuf();
// seek to the beginning
file.seekg(0);
// print contents the second time
std::cout << file.rdbuf();
}
int main (int argc, char* argv[])
{
// print all files passed as a command-line argument twice
for (int i=1; i<argc; ++i) {
printFileTwice(argv[i]);
}
}Ignore up to 10 characters or until first space is found
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
ifstream in("test");
if(!in) {
cout << "Cannot open file.\n";
return 1;
}
in.ignore(10, " ");
char c;
while(in) {
in.get(c);
if(in) cout << c;
}
in.close();
return 0;
}Read and display a text file line by line.
#include <iostream>
#include <fstream>
using namespace std;
int main(int argc, char *argv[])
{
ifstream in("test.txt");
if(!in) {
cout << "Cannot open input file.\n";
return 1;
}
char str[255];
while(in) {
in.getline(str, 255); // delim defaults to "\n"
if(in) cout << str << endl;
}
in.close();
return 0;
}R 9.9 T 9.9 M 4.8
12. 8. 5. Reading a text file
#include <iostream.h>
#include <fstream.h>
#include <stdlib.h>
int main () {
char buffer[256];
ifstream examplefile ("test.txt");
if (! examplefile.is_open())
{
cout << "Error opening file";
exit (1);
}
while (! examplefile.eof() )
{
examplefile.getline (buffer,100);
cout << buffer << endl;
}
return 0;
}
This is a line. This is another line.
Reading numbers from a file
#include <fstream>
#include <iostream>
#include <iomanip>
using std::cout;
using std::endl;
int main() {
const char* filename = "test.txt";
std::ifstream inFile(filename);
// Make sure the file stream is good
if(!inFile) {
cout << endl << "Failed to open file " << filename;
return 1;
}
long n = 0;
while(!inFile.eof()) {
inFile >> n;
cout << std::setw(10) << n;
}
cout << endl;
return 0;
}0 1 2 3 4 5 6 7 8 9 10 11 12 13
14 15 16 17 18 19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34 35 36 37 38 39 40 41
42 43 44 45 46 47 48 49 50 51 52 53 54 55
56 57 58 59 60 61 62 63 64 65 66 67 68 69
70 71 72 73 74 75 76 77 78 79 80 81 82 83
84 85 86 87 88 89 90 91 92 93 94 95 96 97
98 99
Show a file from starting offset
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
int main(int argc, char *argv[])
{
char ch;
ifstream in("test.txt", ios::in | ios::binary);
if(!in) {
cout << "Cannot open file.";
return 1;
}
in.seekg(2, ios::beg);
while(in.get(ch))
cout << ch;
return 0;
}9.9 T 9.9a M 4.8
Use ifstream.read() and ofstream.write()
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
int n[5] = {1, 2, 3, 4, 5};
register int i;
ofstream out("test", ios::out | ios::binary);
if(!out) {
cout << "Cannot open file.\n";
return 1;
}
out.write((char *) &n, sizeof n);
out.close();
for(i=0; i<5; i++) // clear array
n[i] = 0;
ifstream in("test", ios::in | ios::binary);
if(!in) {
cout << "Cannot open file.\n";
return 1;
}
in.read((char *) &n, sizeof n);
for(i=0; i<5; i++) // show values read from file
cout << n[i] << " ";
in.close();
return 0;
}1 2 3 4 5
