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Use of File Stream
Assume ifle and ofile is the string object storing the names of input and output files‘ namess.
string ifile = "inputFile.txt"; string ofile = "outputFile.txt";
Then the use of file stream is like this:
// construct an ifstream and bind it to the file named ifile ifstream infile(ifile.c_str()); // ofstream output file object to write file named ofile ofstream outfile(ofile.c_str());
Also, we can define unbound input and output file stream first, and then use open function to boud the file we‘ll access:
ifstream infile; // unbound input file stream
ofstream outfile; // unbound output file stream
infile.open("in"); // open file named "in" in the current directory
outfile.open("out"); // open file named "out" in the current directory
After opening the file, we need to check if it is successful being opened:
// check that the open succeeded
if(!infile){
cerr << "error: unable to open input file: "
<< infile << endl;
return -1;
}
Rebound File Stream with New File
If we want to bound the fstream with another file, we need to close the current file first, and then bound with another file:
ifstream infile("in"); // open file named "in" for reading
infile.close(); // closes "in"
infile.open("next"); // open file named "next" for reading
Clear File Stream Status
Opening all file names in a string vector, one direct version is:
vector<string> files;
...
vector<string>::const_iterator it = files.begin();
string s; // string buffer
// for each file in the vector
while(it != files.end()){
ifstream input(it->c_str()); // open the file
// if the file is ok, read and "process" the input
if(!input)
break; // error: bail out!
while(input >> s) // do the work on this file
process(s);
++it; // increament iterator to get next file
}
More efficient way but with much more accurate operation version:
ifstream input;
vector<string>::const_iterator it = files.begin();
// for each file in the vector
while(it != files.end()){
input.open(it->c_str()); // open the file
// if the file is ok, read and "process" the input
if(!input)
break; // error: bail out!
while(input >> s) // do the work on this file
process(s);
input.close(); // close file when we‘re done with it
input.clear(); // reset state to ok
++it;
}
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原文地址：http://www.cnblogs.com/kid551/p/4254363.html
