Why is my getline() not reading the first line of my standard input in C?

Question

I'm relatively new to C, and I am uing the getline() function to read the contents of a file supplied as standard input.

However, the while loop does not read the first line of the file & I'm not sure why!

For context: the file reads-

a b c
-d e 
f

And the output reads & splits -d, e & f correctly, but only prints the a b c outside the while loop.

int main (){

//utilising data provided at http://www.linux.die.net/man/3/getline
//char*linePointer is initialized to NULL, for getline() to allocate a buffer that stores the line
//buffer gets resized dynamically 

char *linePointer = NULL; 
size_t len = 0;

//checks if the file is empty and prints -, if it is
if ((getline(&linePointer, &len, stdin) == -1)){
    printf("-\n");
}

//as long as the stream is valid, and the file can be read 
//if either of the conditions are not satisfied then while loop condition is not satisfied 
//prints the contents of the line 

Clauses cs = createNewArrayList();
printf("%s\n", linePointer);
while ((getline(&linePointer, &len, stdin) != -1)){
        printf("%s\n", linePointer);

    Clause c = createNewArrayList();
    char *token; 
    char *delim = " ";
    token = strtok(linePointer, delim);
    while (token != NULL){      
        char *duplicate = strdup(token);     
        add(c, duplicate);
        printf("%s\n",duplicate);
        token = strtok(NULL, delim);
    }
    add(cs, c);
}

free(linePointer);
exit(EXIT_SUCCESS);    

Answer 1

You are reading and discarding the 1st line before entering your while loop, that is why the loop does not see that line.

Try this instead:

int main (){

    //utilising data provided at http://www.linux.die.net/man/3/getline
    //char*linePointer is initialized to NULL, for getline() to allocate a buffer that stores the line
    //buffer gets resized dynamically 

    char *linePointer = NULL; 
    size_t len = 0;

    //checks if the file is empty and prints -, if it is
    if ((getline(&linePointer, &len, stdin) == -1)){
        printf("-\n");
    }
    else{
        //as long as the stream is valid, and the file can be read 
        //if either of the conditions are not satisfied then while loop condition is not satisfied 
        //prints the contents of the line 

        Clauses cs = createNewArrayList();
        do{
            printf("%s\n", linePointer);

            Clause c = createNewArrayList();
            char *delim = " ";
            char *token = strtok(linePointer, delim);
            while (token != NULL){      
                char *duplicate = strdup(token);     
                add(c, duplicate);
                printf("%s\n",duplicate);
                //if add() makes its own copy, then uncomment this,
                //or simply don't use strdup() above to begin with:
                //free(duplicate);
                token = strtok(NULL, delim);
            }
            add(cs, c);

            free(linePointer);
            linePointer = NULL; 
            len = 0;
        }
        while (getline(&linePointer, &len, stdin) != -1);
    }

    free(linePointer);
    exit(EXIT_SUCCESS);
}