C++ File Input/Output Fundamentals
Learn about file input and output operations in C++, including standard input/output, file open modes, buffering, and best practices for handling file operations. Understand how to read from and write to files using ifstream, ofstream, and fstream classes in C++.
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ECE 244 Programming Fundamentals Lec. 5: C++ I/O Ding Yuan ECE Dept., University of Toronto http://www.eecg.toronto.edu/~yuan
Standard input/output #include <iostream> using namespace std; int main() { int x; cout<< Hello world! << endl; cin >> x; } output input Hello world!
File input/output program file file
File input #include <fstream> using namespace std; ifstream inFile( filename ); or ifstream inFile; inFile.open ( filename ); a = 1 b = 2 c = 3 int a,b,c; inFile >> a >> b >> c; 1 2 3 if in ifstream stands for input and file
File output #include <fstream> using namespace std; ofstream outFile( filename ); or ofstream outFile; outFile.open ( filename ); int a = 6; outFile << a = << a << endl; a = 6
Two ways to open a file for output Open for writing (default) If the file already exists, it is first erased; Otherwise it is created Open for append Use: outFile.open( filename , ios::app); Write adds to the end of the file
When opening file inFile.open ( filename ); <- search in current directory inFile.open ( dir/filename ); <- relative path inFile.open ( ../filename ); <- relative path inFile.open ( /etc/passwd ); <- absolute path Question: why do we need to open a file?
You open, you close! When done reading/writing to a file, close it! inFile.close(); outFile.close();
Buffering Output will not be immediately written to file Instead, temporarily store the output in buffer; write out to file periodically in chunks Why buffering? To force output: outFile.flush(); or outFile << endl; outFile << Hello \n ; .. outFile << Hello again! ; Buffer: Hello Hello again! Slow! file
