Novice C language problem: how to pass an array of variable length between function?-CodePudding

I haven't written a C

, I have to do now is: in the function 1 defines a variable length arrays, and then back to the main function, the function USES the array in the 2,
I wrote a program, a simple two problems:
(1) using the malloc defines the variable-length array arr, can not access the arr [1] arr [2] and other elements, can only access arr [0],
Pass into the function value of 2 (2) is completely wrong, seems to be random values,
Master looked glad, thank you!

#include
#include

Struct array
{
int n;
Int * arr;
};

The static struct array * func1 ();
Static int func2 (struct array *);

Struct array * func1 ()
{
Struct array * p1;
Struct array p1_t;
Int I, n;

N=16;//assume n will change -based on user input
P1=& amp; P1_t;
P1 - & gt; N=n;
P1 - & gt; Arr=(int *) malloc (sizeof (int) * n);
For (I=1; I & lt;=n; I++) p1 - & gt; Arr (I - 1]=I;

Return p1;
}

Int func2 (struct array * p2)
{
Int I, n;

N=p2 - & gt; n;
For (I=1; I & lt;=n; I++) p2 - & gt; Arr=n + 1 - [I - 1] I;

return 1;
}

Int main ()
{
Struct array * p;
Int I, n;

P=func1 ();
N=p - & gt; n;
For (I=1; I & lt;=n; I++) printf (" % d ", p - & gt; Arr] [I - 1);
Printf (" after func1. \ n ");
Func2 (p);
For (I=1; I & lt;=n; I++) printf (" % d ", p - & gt; Arr] [I - 1);
Printf (" after func2. \ n ");

return 1;
}

CodePudding user response:

 # include & lt; stdio.h> 
#include  

Struct array 
{
int n; 
Int * arr; 
}; 

The static struct array * func1 (); 
Static int func2 (struct array *); 

Struct array * func1 () 
{
# if 0 
Struct array * p1; 
Struct array p1_t; 
Int I, n; 

N=16;//assume n will change -based on user input 
P1=& amp; P1_t; 
P1 - & gt; N=n; 
P1 - & gt; Arr=(int *) malloc (sizeof (int) * n); 
For (I=1; I & lt;=n; I++) p1 - & gt; Arr (I - 1]=I; 
Return p1;//returns the p1_t address, the address is the address of the local variable, according to a local variable life cycle is this function, so the return of p1 is invalid, also lead to memory leaks, because malloc didn't release, 
# the else 
Struct array * p1; 
Int n, I; 

P1=(struct array *) malloc (sizeof (struct array)); 
if (! (p1) 
exit(0); 

N=16; 
P1 - & gt; N=n; 
P1 - & gt; Arr=(int *) malloc (sizeof (int) * n); 
if (! P1 - & gt; Arr) {
Free (p1); 
exit(0); 
} 
For (I=1; i<=n; I++) 
P1 - & gt; Arr (I - 1]=I; 

Return p1; 

# endif 
} 

Int func2 (struct array * p2) 
{
Int I, n; 

N=p2 - & gt; n; 
For (I=1; I & lt;=n; I++) 
The p2 - & gt; Arr=n + 1 - [I - 1] I; 

return 1; 
} 

Int main () 
{
Struct array * p; 
Int I, n; 

P=func1 (); 
N=p - & gt; n; 
For (I=1; I & lt;=n; I++) 
Printf (" % d ", p - & gt; Arr] [I - 1); 
Printf (" after func1. \ n "); 
Func2 (p); 
For (I=1; I & lt;=n; I++) 
Printf (" % d ", p - & gt; Arr] [I - 1); 
Printf (" after func2. \ n "); 

Free (p - & gt; Arr); 
free(p); 

return 1; 
}

For your reference ~

CodePudding user response:

I'm thinking about you and this is not an array variable but linked list, you can find out how to write list