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File Input and Output
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 ifileifstream infile(ifile.c_str());// ofstream output file object to write file named ofileofstream 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 streamofstream outfile; // unbound output file streaminfile.open("in"); // open file named "in" in the current directoryoutfile.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 succeededif(!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 readinginfile.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 vectorwhile(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 vectorwhile(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;}
File Input and Output
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