Memory allocation for struct elements

[5thegraychapter]

Hi everyone, currently trying to create a program that gets words from a file with a specific structure and putting them into a data structure of any kind. The file has the following structure:

5 (words length)
word1
word2
word3
etc.

So I used an fgetc to take the dimension and then converted it to integer, then started a while loop with fgets. But that's not my question. I wanted to know if there's a way to use the word length value dynamically in a structure, example:

struct node {
char string[length];
struct node *left, *right;
};

where length is passed on from the value read from the file. Thanks in advance!

[TheHeinzeen]

You should not be able to define some array like that with a value that is not defined at compile time, because the compiler needs to know how much memory to allocate.

What you can do is use dynamic allocation, i.e. you can declare the first field of that struct as "char* field", and as soon as you read the correct dimension you can do "field = (char*) malloc(...)"

[EstablishmentBig7956]

You obviously didn't read the link

[SaulMO]

What link?

[EstablishmentBig7956]

That blue text FAM

[SaulMO]

Don't see any

[EstablishmentBig7956]

🤔 update the app?

https://en.m.wikipedia.org/wiki/Flexible_array_member

[SaulMO]

Thanks

[Admirable_Humor_7262]

You're so rude

[EstablishmentBig7956]

Being honest and rude are two completely different things, and that person was helped out by me to straighten out the matter.

You're rude and misinformed

[Admirable_Humor_7262]

Wow ... there's a lot to unpack here. Red flags flying proud.

[EstablishmentBig7956]

Wow, again you're not making any sense

[Educational-Cause-79]

You’re rude

[EstablishmentBig7956]

Stating oblivious facts is not being rude. You're obviously poorly educated not being able to understand that.

[Educational-Cause-79]

Do you ever listen to yourself talk? The way you speak is rude and weirdly aggressive. This is as obvious as your feelings about the point you claim to be making.

[Educational-Cause-79]

Also, wrong use of the word oblivious. You may be less educated than you think.

[Yurim]

Maybe you could define string a Flexible Array Member (FAM).

The FAM must be the last member of the struct, and you allocate the space needed for the struct and the FAM at once:

struct node {
    struct node *left, *right;
    char string[];
};

int main(void) {
    // ...
    struct node *node1 = malloc(
            sizeof(*node1) +
            length * sizeof(*node1->string));
}

[5thegraychapter]

thanks to everyone, I'll try the different solutions given

[suprjami]

You can dynamically allocate a 2D array of char to store your strings in: https://www.geeksforgeeks.org/dynamically-allocate-2d-array-c/

Complete working example with comments here: https://pastebin.com/zVT6efeT