Why does sscanf reads only two lines with pointer to pointer?

Question

I have a file with 10 lines, and in each line there is, separated by spaces, a name, an id and an age. Problem is that when reading this file with fgets and sscanf, it returns me a seg fault when trying to read more than 2 lines.

typedef struct Person
{
    char t;
    long i;
    float a;
} Person;



*arrPersons = (Person*)malloc(10 * sizeof(Person));

int assignInputPeople(Person **arrPersons,  FILE *inputPeople)
{
    int counter = 0;
    char fileLine[344];
    long ID;
float ageF;
 while (fgets(fileLine, 344, inputPeople) != NULL)
    {
        sscanf(fileLine, "%s %s %s", arrPersons[counter]->name,&ID)
   
    
}

I created a pointer to pointer for my array so that I can modify it in other functions, like this one above.

Please post a [Minimal, Reproducible Example](https://stackoverflow.com/help/minimal-reproducible-example) including the caller of `assignInputPeople` and the left part of `assignInputPeople`. — MikeCAT, Aug 02 '20 at 10:35
And in C you don't have to (and really shouldn't) [cast the result of `malloc`](https://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc). — Some programmer dude, Aug 02 '20 at 10:36

score 2 · Accepted Answer · answered Aug 02 '20 at 10:41

2

If you are passing the address of arrPersons in the main() function as the argument arrPersons of the assignInputPeople() function, arrPersons[counter]->name is wrong because what is pointed at by arrPersons have only room for one elemnet, so it is out-of-range when counter is not 0.

In this case, it should be (*arrPersons)[counter].name.

answered Aug 02 '20 at 10:41

MikeCAT

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Where the line `*arrPersons = (Person*)malloc(10 * sizeof(Person))` actually is? – MikeCAT Aug 02 '20 at 10:44
1

Also what is `capacity`? – MikeCAT Aug 02 '20 at 10:45
Just do you know why I have a warning saying that my fields aren't used in my struct ? – MM1 Aug 02 '20 at 11:08
It should be because your fields aren't used. – MikeCAT Aug 02 '20 at 11:09
But when using sscanf , I use them in order to store the data in the line, like for (*arrPersons)[counter].id , or doesn't it count as accessed ? – MM1 Aug 02 '20 at 11:12
Your posted code doesn't contain that. Please post a [Minimal, Reproducible Example](https://stackoverflow.com/help/minimal-reproducible-example). – MikeCAT Aug 02 '20 at 11:13
[Coundl't reproduce](https://wandbox.org/permlink/ucbSUJNxXp50jBus) after adding some tweaks to make it compile. I'd answer "No" for the question "do you know". – MikeCAT Aug 02 '20 at 11:21

Why does sscanf reads only two lines with pointer to pointer?

1 Answers1