sscanf and printf overwriting values - c

Question

I am writing a simple c program that reads in a bunch of values from stdin using getline and sscanf.
The program apparently works: I invoke the function reading the line and print the results with printf. The problem arises when I just tried to print the values again, and the output is gibberish!
-------------------------- EDIT -----------------------------
I found the problem, reported in my own answer below. Thanks everyone for pointing me in the right direction!
My test input file is (with the 2 first lines to be skipped):
//---------------------------------------------------------------------------------
// MODEL VALUE
500 // X DIR
600 // Y DIR
10.0 // Grid Spacing
2e-4 // Time step
80001 // Max run iterations
And my code is:
Functions to read different kinds (separate from main just for clearness in the post)
int readint(void)
{
char *line = NULL;
size_t size;
int my_int;
getline(&line, &size, stdin);
sscanf(line,"%d",&my_int);
return my_int;
}
double readfloat(void)
{
char *line = NULL;
size_t size;
float my_float;
getline(&line, &size, stdin);
sscanf(line,"%f",&my_float);
return my_float;
}
char* readstr(void)
{
char *line = NULL;
size_t size;
getline(&line, &size, stdin);
char * token = strtok(line, " ");
return token;
}
int readvoid(void)
{
char *line = NULL;
size_t size;
getline(&line, &size, stdin);
return 0;
}
Main
#include <stddef.h>
#include <stdio.h>
#include <string.h>
int main(void)
{
int dum;
//- read in input file
//---------------------------------------------------------------------------------
// MODEL VALUE
dum=readvoid();
dum=readvoid();
#define Nx (readint()) // run on 64 nodes
#define Ny (readint()) // Y DIR
#define dx (readfloat()) // Grid Spacing
#define dt (readfloat()) // Time step
#define Max_Time (readint()) // Max run iterations
printf("model: %d,%d,%f,%f,%d\n",Nx,Ny,dx,dt,Max_Time);
printf("model: %d,%d,%f,%f,%d\n",Nx,Ny,dx,dt,Max_Time);
printf("model: %d,%d,%f,%f,%d\n",Nx,Ny,dx,dt,Max_Time);
return 0;
}
With the first printf working just fine and the others outputting random values.
What am I doing wrong? I am new to c but have experience in fortran, shell, python, matlab and am a bit lost.

Answer 1

Of course the responses are "gibberish". my_int is not initialized, so if sscanf does not read a value, then readint is returning an uninitialized variable. (aka, "gibberish"). Since you've already read the file and not rewound, getline is (probably) returning -1 and sscanf is not assigning a value. But you can't tell, because your program does not check the values returned by either getline or sscanf.
You need to rewind the stream if you want to read it again.
Also, you cannot interleave the calls to readint and readfloat in the parameters list of printf. The order in which they will be called is not fixed.

Answer 2

I found out the problem, thanks to above comments:
I naively thought that #define was able to read the output of e.g. readint() and store it as an object-like macro (e.g. #define Nx 500), but apparently this is not the case.
Thanks everyone!