warning: implicit declaration of function 'getline'

Question

Hi I'm almost done with a project I have for class. I need to sort the priority of people in an airline based on a few factors. This is my project description:

"An airline company uses the formula shown below to determine the priority of passengers on the waiting list for overbooked flights. Priority Number = (A / 1000) + B - C where A is the customer’s total mileage in the past year B is the number of years in his or her frequent flier program C is a sequence number representing the customer’s arrival position when he or she booked the flight. Given a file of overbooked customers as shown in the table below, write a program that reads the file and determines each customer’s priority number. The program then builds a priority queue using the priority number and prints a list of waiting customers in priority sequence."

I feel my code encompasses the main idea, but I am having issues with getline. When I compile the code (shown below) it gives me an error: "|24|warning: implicit declaration of function 'getline' [-Wimplicit-function-declaration]|"

Please help me fix this so it will compile. I've tried a lot of things and nothing works.

Here is the code:

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
    FILE * fp; //create file pointer to be read later
    char * line = NULL;
    int temp,count=0,len=0,mileage[100],read,years[100],sequence[100],priority[100];
    char name[100][100],tempst[100];
    fp = fopen("customers.txt", "r"); //opening the file

    if (fp == NULL)
        exit(EXIT_FAILURE);
    int i;



    while ((read = getline(&line, &len, fp)) != -1) { //start reading file and recording data
        i=0;

        while(line[i]!=' ' || (line[i+1]>='A' && line[i+1]<='z'))
        {
            name[count][i]=line[i];
            i++;
        }
        name[count][i++]='\0';
        mileage[count]=0;

        while(line[i]!=' ')
        {
            mileage[count]=mileage[count]*10+(line[i]-'0');
            i++;
        }
        i++;
        years[count]=0;

        while(line[i]!=' ')
        {
            years[count]=years[count]*10+(line[i]-'0');
            i++;
        }
        i++;
        sequence[count]=0;

        while(line[i]!='\0')
        {
            sequence[count]=sequence[count]*10+(line[i]-'0');
            i++;
        }
        priority[count]=(mileage[count]/1000)+years[count]-sequence[count];
        count++;

    }

    for( i=0;i<count-1;i++) // calculate priority
    {
        for(int j=i+1;j<count;j++)
        {
            if(priority[i]<priority[j])
            {
                temp=priority[i];
                priority[i]=priority[j];
                priority[j]=temp;
                strcpy(tempst,name[i]);
                strcpy(name[i],name[j]);
                strcpy(name[j],tempst);
            }
        }
    }

    for( i=0;i<count;i++) //print priority
    {
        printf("%s %d\n",name[i],priority[i]);
    }
    return 0;
}

Answer 1

#define  _GNU_SOURCE
#include <stdio.h>

or

#define  _POSIX_C_SOURCE 200809L
#include <stdio.h>

should get you getline on GNU systems, but there might be another way to enable it on a different POSIX system.

After enabling getline like that, the len variable should be typed size_t, not int so that &len is correctly typed as size_t *.

It is possible that your project testing software doesn't support the getline POSIX function in which case you might need to rethink your design in terms of standard C functions instead.