How do you open a file in C++?

Question

I want to open a file for reading, the C++ way. I need to be able to do it for:

• text files, which would involve some sort of read line function.

Answer 1

To open and read a text file line per line, you could use the following:

// define your file name
string file_name = "data.txt";

// attach an input stream to the wanted file
ifstream input_stream(file_name);

// check stream status
if (!input_stream) cerr << "Can't open input file!";

// file contents  
vector text;

// one line
string line;

// extract all the text from the input file
while (getline(input_stream, line)) {

    // store each line in the vector
    text.push_back(line);
}

To open and read a binary file you need to explicitly declare the reading format in your input stream to be binary, and read memory that has no explicit interpretation using stream member function read():

// define your file name
string file_name = "binary_data.bin";

// attach an input stream to the wanted file
ifstream input_stream(file_name, ios::binary);

// check stream status
if (!input_stream) cerr << "Can't open input file!";

// use function that explicitly specifies the amount of block memory read 
int memory_size = 10;

// allocate 10 bytes of memory on heap
char* dynamic_buffer = new char[memory_size];

// read 10 bytes and store in dynamic_buffer
file_name.read(dynamic_buffer, memory_size);

When doing this you'll need to #include the header :