Thread: pass by value / passy by reference

You need to pass a pointer to emp if you want the called function to change its value in the calling function.

Code:

readname (fin, a, &emp);

Code:

void readname(FILE* fin, struct emp a[], int *num_emp) {        
        
        fscanf(fin, "%d", num_emp);        
       
        printf("%d", *num_emp);
}

By the way, the size of the array is unnecessary; the compiler will treat struct emp a[1024], struct emp a[], or struct emp *a as just a pointer to a struct emp. Also, although I guess it's legal to have both a struct emp and an int emp in your program, it seems unnecessarily confusing. Why not use a different (and more descriptive) name for the int, such as int num_emp as you did in readname()?

Originally Posted by R.Stiltskin

Also, although I guess it's legal to have both a struct emp and an int emp in your program, it seems unnecessarily confusing. Why not use a different (and more descriptive) name for the int, such as int num_emp as you did in readname()?

i have it named that in the actual code i just changed it to set the function call apart from the function more clearly. i didnt realize i made the struct and the int both the same name.

i tried exactly what you posted a few times and i get the same output plus a [warning] "comparison between pointer and integer"

Originally Posted by ominub

i tried exactly what you posted a few times and i get the same output plus a [warning] "comparison between pointer and integer"

That does not relate to the code we have posted here. There must be something wrong elsewhere in the program (the warning should tell you which line). In the code I posted, I assumed that in the calling function, num_emp is defined as
int num_emp, NOT int *num_emp. Which is it?

Warning is because when you pass &emp to the function, you have to use *num_emp for the comparison.

then it just crashes and doesn't print anything. no errors or warnings just a pop up window that says the program has stopped working.

Post the code that crashed.

PM okay? its an open assignment.

Just post the same section as before, after the changes you made.

Code:

void readempname(FILE* fin, struct employee a[1024], int *num_emp) ;

int main() {

    int emp;

        readempname(fin, a, &emp);

        printf("%d\n", emp);

}


void readempname(FILE* fin, struct employee a[1024], int *num_emp)  {

int     i=0;
    
        // read in  # of employees
        fscanf(fin, "%d", &num_emp);
        
        //read in first name / last name / pph
        for (i = 0; i < *num_emp; i++) {         
            fscanf(fin, "%s", a[i].first);
            fscanf(fin, "%s", a[i].last);
            fscanf(fin, "%lf", &a[i].payperhr);
        }

        printf("%d\n", num_emp);
}

The only error I see there is that you forgot to change num_emp to *num_emp in the last printf statement, but that shouldn't cause it to crash. I suggest you move that printf statement to immediately after the fscanf that reads in the value for num_emp, just to be sure that the input is OK (it should print before it crashes). Then you can start looking for the next error someplace else.

i put the printf right after the fscanf and it still crashed without printing num_emp

Sorry, I just looked again at the code you posted in #11. You also forgot to change the fscanf statement in readempname(). Look at my code in post #2 more carefully. num_emp is already a pointer, so you shouldn't be using the & operator there.