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What is a good approach to read the whole file content in a buffer for C++?

While in plain C I could use fopen(), fseek(), fread() function combination and read the whole file to a buffer, is it still a good idea to use the same for C++? If yes, then how could I use RAII approach while opening, allocating memory for buffer, reading and reading file content to buffer.

Should I create some wrapper class for the buffer, which deallocates memory (allocated for buffer) in it's destructor, and the same wrapper for file handling?

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3 Answers 3

Reset to default
101

There's no need for wrapper classes for very basic functionality:

std::ifstream file("myfile", std::ios::binary | std::ios::ate);
std::streamsize size = file.tellg();
file.seekg(0, std::ios::beg);

std::vector<char> buffer(size);
if (file.read(buffer.data(), size))
{
    /* worked! */
}
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8 Comments

Wouldn't uint8_t be better than char?
Jamie - read() returns a reference to the ifstream itself. By using it in a boolean context, you implicitly call operator bool(), which returns the same as !fail() => this code is correct
You can't rely on tellg() for the file size, AFAICR.
if the file is binary, that works. If it's text, then yes you cannot.
He said you do not use tellg() to get the file size.
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42

You can access the contents of a file with a input file stream std::ifstream, then you can use std::istreambuf_iterator to iterate over the contents of the ifstream,

std::string
getFileContent(const std::string& path)
{
  std::ifstream file(path);
  std::string content((std::istreambuf_iterator<char>(file)), std::istreambuf_iterator<char>());

  return content;
}

In this case im using the iterator to build a new string using the contents of the ifstream, the std::istreambuf_iterator<char>(file) creates an iterator to the begining of the ifstream, and std::istreambuf_iterator<char>() is a default-constructed iterator that indicate the special state "end-of-stream" which you will get when the first iterator reach the end of the contents.

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Comments

26

Something I have in most of my programs:

/** Read file into string. */
inline std::string slurp (const std::string& path) {
  std::ostringstream buf; 
  std::ifstream input (path.c_str()); 
  buf << input.rdbuf(); 
  return buf.str();
}

Can be placed in a header.
I think I have found it here: https://stackoverflow.com/a/116220/257568

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2 Comments

Great function name!
Thanks! The name comes up in Perl.

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