fstream

2010-4-5 wcdj
There are three files, named as a, b, c respectively. Now we read every word in these files and push each word into a vector, and then print the contents to the standard output.
[a.txt]
Hello everyone! I am glad to have
a chance to introduce myself.
[b.txt]
My name is wcdj, I am from Luo Yang He Nan province that
is a beautiful city is known as peony hometown and Long Men Grotto.
[c.txt]
So welcome to my hometown, that's all, thank you!

[1]

/* if some file unable to open, it will return -1 */ #include <iostream> #include <string> #include <vector> #include <iterator> #include <fstream> using namespace std; // VC6 does not support C++ standard well // using std::cin; // using std::cout; // using std::cerr; // using std::endl; // using std::string; // using std::vector; // using std::ifstream; int main() { vector<string> svec_file,svec_content; svec_file.push_back("c://a.txt"); svec_file.push_back("c://b.txt"); svec_file.push_back("c://c.txt"); ifstream input; vector<string>::const_iterator it=svec_file.begin(); string word; // for each file in the vector while (it!=svec_file.end()) { // use the member c_str of string class to obtain a C-style string input.open(it->c_str());// open the file if (!input) { cerr<<"error: unable to open input file: "<<it->c_str()<<endl; return -1; } while (input>>word)// do the work on this file { svec_content.push_back(word); svec_content.push_back(" ");// separate every word } // prevent the IO error happening input.close();// close file when we're done with it input.clear();// reset state to ok ++it;// increment iterator to get next file } // read and print the contents in these file from svec_content vector<string>::const_iterator iter=svec_content.begin(); while (iter!=svec_content.end()) { cout<<*iter++; } cout<<endl<<"------end------"<<endl; return 0; } /* output: Hello everyone! I am glad to have a chance to introduce myself. My name is wcdj, I am from Luo Yang He Nan province that is a beautiful city is known as peony hometown and Long Men Grotto. So welcome to my hometown, that's all, thank you! ------end------ Press any key to continue */

[2]

/* if some file is unable to open, it will open next file */ #include <iostream> #include <string> #include <vector> #include <iterator> #include <fstream> using namespace std; // VC6 does not support C++ standard well // using std::cin; // using std::cout; // using std::cerr; // using std::endl; // using std::string; // using std::vector; // using std::ifstream; int main() { vector<string> svec_file,svec_content; svec_file.push_back("c://a.txt"); svec_file.push_back("c://b.txt");// assuming b.txt unable to open svec_file.push_back("c://c.txt"); ifstream input; vector<string>::const_iterator it=svec_file.begin(); string word; // for each file in the vector while (it!=svec_file.end()) { // use the member c_str of string class to obtain a C-style string input.open(it->c_str());// open the file if (!input) { cerr<<"error: unable to open input file: "<<*it<<endl; input.clear();// reset state to ok ++it;// continue to open next file } else { while (input>>word)// do the work on this file { svec_content.push_back(word); svec_content.push_back(" ");// separate every word } // prevent the IO error happening input.close();// close file when we're done with it input.clear();// reset state to ok ++it;// increment iterator to get next file } } // read and print the contents in these file from svec_content vector<string>::const_iterator iter=svec_content.begin(); while (iter!=svec_content.end()) { cout<<*iter++; } cout<<endl<<"------end------"<<endl; return 0; } /* output: error: unable to open input file: c:/b.txt Hello everyone! I am glad to have a chance to introduce myself. So welcome to my hometown, that's all, thank you! ------end------ Press any key to continue */

[3]

/* Modify the codes to read a line from each file. We are able to use getline() function to make it. */ #include <iostream> #include <string> #include <vector> #include <iterator> #include <fstream> using namespace std; // VC6 does not support C++ standard well // using std::cin; // using std::cout; // using std::cerr; // using std::endl; // using std::string; // using std::vector; // using std::ifstream; int main() { vector<string> svec_file,svec_content; svec_file.push_back("c://a.txt"); svec_file.push_back("c://b.txt"); svec_file.push_back("c://c.txt"); ifstream input; vector<string>::const_iterator it=svec_file.begin(); string word; // for each file in the vector while (it!=svec_file.end()) { // use the member c_str of string class to obtain a C-style string input.open(it->c_str());// open the file if (!input) { cerr<<"error: unable to open input file: "<<*it<<endl; input.clear();// reset state to ok ++it;// continue to open next file } else { while (getline(input,word))// do the work on this file { svec_content.push_back(word); svec_content.push_back(" ");// separate each line } // prevent the IO error happening input.close();// close file when we're done with it input.clear();// reset state to ok ++it;// increment iterator to get next file } } // read and print the contents in these file from svec_content vector<string>::const_iterator iter=svec_content.begin(); while (iter!=svec_content.end()) { cout<<*iter++; } cout<<endl<<"------end------"<<endl; return 0; } /* output: Hello everyone! I am glad to have a chance to introduce myself. My name is wcdj, I am from Luo Yang He Nan province that is a beautiful city is known as peony hometown and Long Men Grotto. So welcome to my hometown, that's all, thank you! ------end------ Press any key to continue */