Материал из C\C++ эксперт
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change a file by offset
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
int main(int argc, char *argv[])
{
fstream out("test.txt", ios::in | ios::out | ios::binary);
if(!out) {
cout << "Cannot open file.";
return 1;
}
out.seekp(12, ios::beg);
out.put("a");
out.close();
return 0;
}Open a file for output then write to that file
#include <fstream>
#include <iostream>
using namespace std;
int main ()
{
char buffer[256];
// open it for output then write to it
fstream myfile;
myfile.open("test.txt",ios::out | ios::trunc);
if (myfile.is_open()) {
myfile << "This outputting a line.\n";
myfile.close();
}
return 0;
}Reverse a file
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
int main(int argc, char *argv[])
{
fstream inout("test.txt", ios::in | ios::out | ios::binary);
if(!inout) {
cout << "Cannot open input file.\n";
return 1;
}
long e, i, j;
char c1, c2;
e = 5;
for(i=0, j=e; i<j; i++, j--) {
inout.seekg(i, ios::beg);
inout.get(c1);
inout.seekg(j, ios::beg);
inout.get(c2);
inout.seekp(i, ios::beg);
inout.put(c2);
inout.seekp(j, ios::beg);
inout.put(c1);
}
inout.close();
return 0;
}Use fstream to read and write a file.
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
char ch;
fstream finout("test.dat");
if(!finout) {
cout << "Cannot open file for output.\n";
return 1;
}
for(int i=0; i < 3; ++i) finout.put("X");
if(!finout.good()) {
cout << "Error occurred while writing to the file.\n";
return 1;
}
finout.flush();
cout << "Here are the next ten characters: ";
for(int i=0; i < 10; ++i) {
finout.get(ch);
cout << ch;
}
cout << endl;
if(!finout.good()) {
cout << "Error occurred while reading from the file.\n";
return 1;
}
finout.close();
if(!finout.good()) {
cout << "Error occurred while closing the file.\n";
return 1;
}
return 0;
}
