fscanf in C segmentation error

Question

I am trying to read in values from a file and store them in a structure.

The structure contains

char region
char country[100]
int country_code

The instance of this structure is called c[100]

The file i am trying to read in looks like this

Europe
0 France
1 England
2 Germany

There are an unkonwn number of countries, so it has keep reading until EOF.

I have created an array of the structures.

The code i have so far looks like this:

fp= fopen(countries,"r");

    while (!feof(fp))
    {
    fscanf(fp, "%[^\n]", c.region);
        while (!feof(fp))
        {
        fscanf(fp, "%d, %[^\n]", c[i].country_code, c[i].country);
        i++;
        }
    }

I get a segmentation fault. I'm sure its something obvious that ive missed out or done wrong, but im not sure what, and i would be grateful if anyone could help.

Solution 1

fscanf(myfile, "%d, %[^\n]", c[i].country_code, c[i].country);

should be fixed to

fscanf(myfile, "%d, %[^\n]", &(c[i].country_code), c[i].country);

as fscanf needs an address to write data. You do not need to use & for char array, as it is already a pointer.

Also, in your structure char region; should be changed to char region[100]; as you have not the one char for the region, but several ones, IOW a string.

Solution 2

 myfile = fopen(countries,"r");

Check the return value for errrs

while (!feof(myfile))
{
fscanf(myfile, "%[^\n]", c.region);

You need to pass the address of c.region: &c.region. However, it's still wrong as you're only allocating one character and fscanf will read characters until a non-match. You should change the declaration of c.region to be a character array c.region[[00] or something.

Also, c is an array, not a struct, so I don't think this is the code you're actually using. Did you mean c[0].region?

You should also worry about reading more than whatever you have allocated. Read up on fscanf's ways of limiting what it stores in the address passed

Where do you set i to zero?

    while (!feof(myfile))
    {
    fscanf(myfile, "%d, %[^\n]", c[i].country_code, c[i].country);

Again, you need to pass the address of the country_code field &c[i].country_code" . Note that you do not need to use the & operator on the country field, even though the other answers so far say you do as country is a char array and so c[i].country is the same as &c[i].country

    i++;

What happens if there are more lines in the file than allocated entries in the c[i] array?

Comments

[Vladimir Ivanov]

c[i].country is already a char array, no & here is necessary.

[John Källén]

You're right that there is no need for & for country. However it is not a char, it is an array of char (char[100]). When passing an array of char as a parameter to a function, the compiler converts it into a char pointer (char*).

[user411313]

-1 comma in formatspec is wrong here, fscanf-return are ignored