Weird changing of struct values

[hollow agate]

So, I have seen this kind of behavior few times before but really have no clue about why that would happen

    JsonArrayT *array = JsonArray_new(strlen(expression) / 2);
    printf("%lu %lu\n", array->length, array->allocated);
    char *str = strdup(expression);
    char *token;
    printf("%lu %lu\n", array->length, array->allocated);

output:

0 4
140146654475791 4

why is the value of length changing??

[shrewd parcel]

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[true surge]

whats the context

im assuming you did something wrong with the allocation

maybe made it a pointer to a local variable and its getting corrupted

idk

[ivory violet]

is this your actual code or a contrived example?

[true surge]

@hollow agate give more context

what does JsonArray_new do

[hollow agate]

its just

JsonArrayT *
JsonArray_new(size_t size)
{
    JsonT *array = malloc(sizeof(JsonT) * size);
    return &(JsonArrayT){.array = &array, .length = 0, .allocated = size};
}

I think its because i didn't allocate memory for the return object

[ivory violet]

yeah, that's it

[true surge]

wtf

[ivory violet]

you're returning a pointer to the stack

but after the function exits, you no longer own that memory

[true surge]

yea

[hollow agate]

aha ic

[true surge]

whenever you call a function it makes a new frame

this exists in one frame

then when you call strdup it overwrites the data with garbage

[hollow agate]

ah ok

thanks 👍

[true surge]

why not return JsonArrayT{ .array = array, .length = 0, .allocated = size }

i dont think it needs to be a pointer since the array already is

[hollow agate]

the array inside JsonArrayT is supposed to an array of pointers to JsonT

[true surge]

then youre not doing it right

JsonT **array = malloc(sizeof(JsonT*) * size);

you made a single pointer before

and then pointed to that

[hollow agate]

oh right

[true surge]

[[ json ]] what you had
[[ json ], [ json ], [ json ], ...] what you want

of course now you need to initialize the json pointers as well

id probably have it be an array of json objects

and each of those has a string or whatever in it as a data member

[hollow agate]

thats what i had before, decided to change it for some reason

anyways, thanks for advice 😄

!solved