std::basic_istream::read
From cppreference.com
< cpp | io | basic istream
basic_istream& read( char_type* s, std::streamsize count );
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Extracts characters from stream.
Behaves as UnformattedInputFunction
. After constructing and checking the sentry object, extracts characters and stores them into successive locations 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().
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[edit] Parameters
s | - | pointer to the character array to store the characters to |
count | - | number of characters to read |
[edit] Return value
*this
[edit] Exceptions
If an internal operation throws an exception, it is caught and badbit is set. If exceptions() is set for badbit
, the exception is rethrown.
[edit] 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; raw.read(reinterpret_cast<char*>(&n), sizeof n); std::cout << std::hex << std::showbase << n << '\n'; // prepare file for next snippet std::ofstream os("test.txt", std::ofstream::binary); for (unsigned i = 0; i < 10; i++) { // prepare stream os << "abcd" << i << "\n"; } os.close(); // read entire file into string std::ifstream is("test.txt", std::ifstream::binary); if (is) { // get length of file: is.seekg(0, is.end); int length = is.tellg(); is.seekg(0, is.beg); std::string str; str.resize(length, ' '); // reserve space char* begin = &*str.begin(); is.read(begin, length); is.close(); std::cout << str << "\n"; } else { std::cout << "Could not open test.txt\n"; } }
Output:
0x12121212 abcd0 abcd1 abcd2 abcd3 abcd4 abcd5 abcd6 abcd7 abcd8 abcd9
[edit] See also
inserts blocks of characters (public member function of std::basic_ostream )
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extracts formatted data (public member function) |
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extracts already available blocks of characters (public member function) |
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extracts characters (public member function) |
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extracts characters until the given character is found (public member function) |
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reads from a file (function) |