CODEWITHSUNDEEP
cdata-structuresmemory-management
Qosmo
Qosmo

Reputation: 1202

Memory allocation of global structure

struct ponto *ps = malloc( sizeof(struct ponto) * colunas * linhas );

I had this declared on my main(). However I want it to be globally accessible to all functions. I believe this is made with realloc and declaring this as null or something on the start of the file. Is this correct?

struct ponto *ps = null;

and then, when I know the size that I need for the struct of arrays:

ps = realloc (ps, sizeof(struct ponto) * colunas * linhas);

But this doesn't seem to work hehe. Any tips?

Upvotes: 1

Views: 3147

Answers (2)

Fred Foo
Fred Foo

Reputation: 363707

Making ps globally visible requires that it is a global variable. You probably also need to do this for the number of columns and lines.

struct ponto *ps;
int colunas, linhas;

int main()
{
    colunas = /* whatever */;
    linhas  = /* whatever */;
    ps = malloc(sizeof(struct ponto) * colunas * linhas);
    /* do other stuff */
}

Now ps is visible to all functions in the source file and through it, they can access the memory it points to.

If you have multiple source files, you'll have to tell them about ps in a header file which declares it

struct ponto { /* whatever */ };  /* define the struct in the header */
extern struct ponto *ps;
extern int colunas, linhas;

realloc performs an entirely different operation, it resizes the buffer ps points to. null does not exist in standard C.

Upvotes: 1

jtdubs
jtdubs

Reputation: 13983

If your problem is really just the scope of the variable, you can do this:

struct ponto *ps = NULL;
...
int main()
{
    ps = malloc( sizeof(struct ponto) * colunas * linhas );
    ...
}

Upvotes: 1

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