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std::fread(3)		       C++ Standard Libary		   std::fread(3)

NAME
     std::fread - std::fread

Synopsis
	Defined in header <cstdio>
	std::size_t  fread(  void*  buffer, std::size_t size, std::size_t count,
     std::FILE*
	stream );

	Reads up to count objects into the array buffer  from  the  given  input
     stream stream
	as  if by calling std::fgetc size times for each object, and storing the
     results, in
	the order obtained, into the successive positions of  buffer,  which  is
     reinterpreted
	as an array of unsigned char. The file position indicator for the stream
     is advanced
	by the number of characters read.

	If the objects are not TriviallyCopyable, the behavior is undefined.

	If  an	error occurs, the resulting value of the file position indicator
     for the
	stream is indeterminate. If a partial element is read, its value is  in-
     determinate.

Parameters
	buffer - pointer to the first object in the array to be read
	size   - size of each object in bytes
	count  - the number of the objects to be read
	stream - input file stream to read from

Return value
	Number	of objects read successfully, which may be less than count if an
     error or
	end-of-file condition occurs.

	If size or count is zero, fread returns zero and performs no  other  ac-
     tion.

	fread  does  not  distinguish between end-of-file and error, and callers
     must use
	std::feof and std::ferror to determine which occurred.

Example
     // Run this code

      #include <cstddef>
      #include <cstdio>
      #include <fstream>
      #include <iomanip>
      #include <iostream>
      #include <vector>

      int main()
      {
	  // Prepare file
	  std::ofstream("test.txt") << 1 << ' ' << 2 << '\n';
	  std::FILE* f = std::fopen("test.txt", "r");

	  std::vector<char> buf(4); // char is trivially copyable
	  const std::size_t n = std::fread(&buf[0], sizeof  buf[0],  buf.size(),
     f);

	  std::cout << "Read " << n << " object" << (n > 1 ? "s" : "") << ": "
		    << std::hex << std::uppercase << std::setfill('0');
	  for (char n : buf)
	      std::cout << "0x" << std::setw(2) << static_cast<short>(n) << ' ';
	  std::cout << '\n';

	  std::vector<std::string> buf2; // string is not trivially copyable
      //  This would result in undefined behavior:
      //  std::fread(&buf2[0], sizeof buf2[0], buf2.size(), f);
      }

Possible output:
      Read 4 objects: 0x31 0x20 0x32 0x0A

See also
	scanf  reads formatted input from stdin, a file stream or a buffer
	fscanf (function)
	sscanf
	fgets  gets a character string from a file stream
	       (function)
	fwrite writes to a file
	       (function)
	C documentation for
	fread

http://cppreference.com 	   2024.06.10			   std::fread(3)
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