std::fgets(3)

NAME
std::fgets - std::fgets

Synopsis
   Defined in header <cstdio>
   char* fgets( char* str, int count, std::FILE* stream );
   Reads at most count - 1 characters from the given file stream and stores them in the
   character array pointed to by str. Parsing stops if a newline character is found, in
   which case str will contain that newline character, or if end-of-file occurs. If
   bytes are read and no errors occur, writes a null character at the position
   immediately after the last character written to str.

Parameters
   str - pointer to an element of a char array
   count - maximum number of characters to write (typically the length of str)
   stream - file stream to read the data from

Return value
   str on success, null pointer on failure.
   If the end-of-file condition is encountered, sets the eof indicator on stream (see
   std::feof()). This is only a failure if it causes no bytes to be read, in which case
   a null pointer is returned and the contents of the array pointed to by str are not
   altered (i.e. the first byte is not overwritten with a null character).
   If the failure has been caused by some other error, sets the error indicator (see
   std::ferror()) on stream. The contents of the array pointed to by str are
   indeterminate (it may not even be null-terminated).

Notes
   POSIX additionally requires that fgets sets errno if it encounters a failure other
   than the end-of-file condition.
   Although the standard specification is unclear in the cases where count <= 1, common
   implementations do
     * if count < 1, do nothing, report error,
     * if count == 1,
     * some implementations do nothing, report error,
     * others read nothing, store zero in str[0], report success.

Example
// Run this code
 #include <cstdio>
 #include <cstdlib>
 #include <iomanip>
 #include <iostream>
 #include <span>
 void dump(std::span<const char> buf, std::size_t offset)
 {
     std::cout << std::dec;
     for (char ch : buf)
         std::cout << (ch >= ' ' ? ch : '.'), offset--;
     std::cout << std::string(offset, ' ') << std::hex
               << std::setfill('0') << std::uppercase;
     for (unsigned ch : buf)
         std::cout << std::setw(2) << ch << ' ';
     std::cout << std::dec << '\n';
 }
 int main()
 {
     std::FILE* tmpf = std::tmpfile();
     std::fputs("Alan Turing\n", tmpf);
     std::fputs("John von Neumann\n", tmpf);
     std::fputs("Alonzo Church\n", tmpf);
     std::rewind(tmpf);
     for (char buf[8]; std::fgets(buf, sizeof buf, tmpf) != nullptr;)
         dump(buf, 10);
 }

Output:
 Alan Tu. 41 6C 61 6E 20 54 75 00
 ring..u. 72 69 6E 67 0A 00 75 00
 John vo. 4A 6F 68 6E 20 76 6F 00
 n Neuma. 6E 20 4E 65 75 6D 61 00
 nn..uma. 6E 6E 0A 00 75 6D 61 00
 Alonzo . 41 6C 6F 6E 7A 6F 20 00
 Church.. 43 68 75 72 63 68 0A 00

See also
   scanf reads formatted input from stdin, a file stream or a buffer
   fscanf (function)
   sscanf
   gets reads a character string from stdin
   (deprecated in C++11) (function)
   (removed in C++14)
   fputs writes a character string to a file stream
                        (function)
   C documentation for
   fgets