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std::basic_istream::read(3) C++ Standard Libary std::basic_istream::read(3) NAME std::basic_istream::read - std::basic_istream::read Synopsis basic_istream& read( char_type* s, std::streamsize count ); Extracts characters from stream. Behaves as UnformattedInputFunction. After constructing and checking the sentry object, extracts characters and stores them into successive loca- tions of the character array whose first element is pointed to by s. Characters are extracted and stored until any of the following conditions occurs: * count characters were extracted and stored * end of file condition occurs on the input sequence (in which case, setstate(failbit|eofbit) is called). The number of successfully extracted characters can be queried using gcount(). Parameters s - pointer to the character array to store the characters to count - number of characters to read Return value *this Exceptions failure if an error occurred (the error state flag is not goodbit) and exceptions() is set to throw for that state. If an internal operation throws an exception, it is caught and bad- bit is set. If exceptions() is set for badbit, the exception is rethrown. Notes When using a non-converting locale (the default locale is non-con- verting), the overrider of this function in std::basic_ifstream may be optimized for zero-copy bulk I/O (by means of overriding std::streambuf::xsgetn) Example // Run this code #include <iostream> #include <fstream> #include <sstream> #include <string> #include <cstdint> int main() { // read() is often used for binary I/O std::string bin = {'\x12', '\x12', '\x12', '\x12'}; std::istringstream raw(bin); std::uint32_t n; if(raw.read(reinterpret_cast<char*>(&n), sizeof n)) std::cout << std::hex << std::showbase << n << '\n'; // prepare file for next snippet std::ofstream("test.txt", std::ios::binary) << "abcd1\nabcd2\nabcd3"; // read entire file into string if(std::ifstream is{"test.txt", std::ios::binary | std::ios::ate}) { auto size = is.tellg(); std::string str(size, '\0'); // construct string to stream size is.seekg(0); if(is.read(&str[0], size)) std::cout << str << '\n'; } } Output: 0x12121212 abcd1 abcd2 abcd3 See also write inserts blocks of characters (public member function of std::basic_os- tream<CharT,Traits>) operator>> extracts formatted data (public member function) readsome extracts already available blocks of characters (public member function) get extracts characters (public member function) getline extracts characters until the given character is found (public member function) fread reads from a file (function) http://cppreference.com 2022.07.31 std::basic_istream::read(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Notes | Example | Output: | See also
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