getline() function error in c++ code - c++

Question

Can someone tell me what am i doing wrong here i am getting an error saying getline() not declared in this scope.........any help would be appreciated.
no matching function for call to getline(char**, size_t*, FILE*&)
#include<iostream>
#include<fstream>
#include<string>
using namespace std;
char *s;
int main(int argc, char *argv[])
{
FILE* fd = fopen("input.txt", "r");
if(fd == NULL)
{
fputs("Unable to open input.txt\n", stderr);
exit(EXIT_FAILURE);
}
size_t length = 0;
ssize_t read;
const char* backup;
while ((read = getline(&s, &length, fd) ) > 0)
{
backup = s;
if (A() && *s == '\n')
{
printf("%sis in the language\n", backup);
}
else
{
fprintf(stderr, "%sis not in the language\n", backup);
}
}
fclose(fd);
return 0;
}

Answer 1

You'll need to use C++ style code in order to use getline in a cross platform way.
#include <fstream>
#include <string>
using namespace std;
std::string s;
bool A() { return true; }
int main(int argc, char *argv[])
{
ifstream myfile("input.txt");
if(!myfile.is_open())
{
fprintf(stderr, "Unable to open input.txt\n");
return 1;
}
size_t length = 0;
size_t read;
std::string backup;
while (getline(myfile, s))
{
backup = s;
if (A() && s == "\n")
{
printf("%s is in the language\n", backup.c_str());
}
else
{
fprintf(stderr, "%s is not in the language\n", backup.c_str());
}
}
return 0;
}

Answer 2

What are you trying to do with getline(&s, &length, fd)? Are you trying to use the C getline?
Assuming you have opened the file correctly, in c++ your getline should look something like this: getline(inputStream, variableToReadInto, optionalDelimiter).
You didn't include <stdio.h> but you did include <fstream>. Maybe use ifstream fd("input.txt");
What's A()
If you ARE trying to use the C getline, the using namespace std may be interfering
Why are you using printf and fprintf and not cout << xxxxxx and fd << xxxxxx

Answer 3

You seem to be a bit confused with various getline function signatures.
The standard C++ std::getline signature is
template< class CharT, class Traits, class Allocator >
std::basic_istream<CharT,Traits>& getline( std::basic_istream<CharT,Traits>& input,
std::basic_string<CharT,Traits,Allocator>& str,
CharT delim );
It takes an input stream object, a string and a character delimiter (there's an overload without the delimiter too).
The posix getline signature is
ssize_t getdelim(char **lineptr, size_t *n, int delim, FILE *stream);
with the delimiter optional again.
now in your code your passing arguments as if calling the posix version without delimiter. If you want to use the standard one you'll have to change the arguments (i.e. istream object instead of FILE*). I don't know if the posix one is even available for you, since posix is different from any C++ standard.
Note that the fputs, FILE*, fprintf are C filehandling functions, not the C++ ones.