warning: array subscript is above array bounds [-Warray-bounds] in module

Question

static int myarray[2]={-1,234};
module_param_array(myarray,int,&arrayargc,0);
MODULE_PARM_DESC(myarray,"Integer Array");

static int __init module_init_2(void)
{
 int i;
  for(i=0;i< (sizeof myarray/sizeof(int));i++);
{

printk(KERN_INFO "myarray[%d] is %d",i,myarray[i]);

}

I am writing a simple module to take some command line input.During compilation it is giving a warning

warning: array subscript is above array bounds [-Warray-bounds]
printk(KERN_INFO "myarray[%d] is %d",i,myarray[i]);

Why is it giving warning as loop seems to be run till i=2, I saw some questions regarding this but that didn't help me so much

You forgot commas between `"Option#N ..."` strings. C takes it as a single string. Voting to close as a typo. — Sergey Kalinichenko, Oct 30 '16 at 11:02
Does not even compile without a warning saying what is wrong. — Weather Vane, Oct 30 '16 at 11:02
I have made it correct. Now the problem is that the program prints the options then bypass the m=getchar and direct jumps to the next printf. Could you please tell me the reason? — Saud Farooqui, Oct 30 '16 at 11:11
Cannot reproduce that, but BTW `char m;` should be `int m;` which is the type returned by `getchar()`. — Weather Vane, Oct 30 '16 at 11:13
@SaudFarooqui That's because you're using `scanf` for user input, which is a mistake. Also, there are about 500 duplicates of this question on SO. — melpomene, Oct 30 '16 at 11:19
@melpomene could you please give me the link for the same problem' — Saud Farooqui, Oct 30 '16 at 11:26
You should use `fgets`. http://stackoverflow.com/search?q=scanf+skip — melpomene, Oct 30 '16 at 11:28
char *o,*m; m=fgets(o,2,stdin); but now it again makes segmentation fault — Saud Farooqui, Oct 30 '16 at 11:36
Having added the two missing commas, I cannot reproduce your next problem. Please ask a new question with the [**Minimal, Complete, and Verifiable example**](http://stackoverflow.com/help/mcve) that shows the problem. "Complete" meaning your code can be copy/pasted into a text editor and compiled exactly as it is, to demonstrate the fault. — Weather Vane, Oct 30 '16 at 11:50

artm · Answer 1 · 2016-10-30T11:09:35.037

3

Your very beginning printf specifies three %s for three strings, yet you provided just one string for that printf, and so the crash.

Note from Weather Vane comment:

Remember that the C compiler will concatenate string literals which are separated only by whitespace.

That means even though you wrote three separate "Option #1", "Option #2", etc. in three lines they still counted as just one string (after concatenation. Fix that by adding a comma at the end of each line to prevent concatenation (and so you'd have three separate strings).

edited Oct 30 '16 at 11:09

answered Oct 30 '16 at 11:02

artm

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Yes you are right, I added your comment which should explain the OP problem much clearer. – artm Oct 30 '16 at 11:10
1

I like the way beginners generate "creative" bugs that you'd never think of. Almost art. – Jean-François Fabre Oct 30 '16 at 11:11
I have made it correct. Now the problem is that the program prints the options then bypass the m=getchar and direct jumps to the next printf. Could you please tell me the reason? – Saud Farooqui Oct 30 '16 at 11:11
`m` should be `int` for `getchar` - other than that it should work ok – artm Oct 30 '16 at 11:15
I have made m int but still it is bypassing – Saud Farooqui Oct 30 '16 at 11:23

score 0 · Answer 2 · answered Oct 30 '16 at 12:39

You can try this. I assumed you want to output both values that are successfully read.

#include <stdio.h>
#include <stdlib.h>

int
main(int argc, char const *argv[]) {
    int period, time;

    const char micro_sec = 'u';
    const char mili_sec = 'm';
    const char sec = 's';

    printf("\nSelect unit of Time period: \n");

    printf("\nOption 1: %c for micro seconds\n"
             "Option 2: %c for mili seconds\n"
             "Option 3: %c for seconds\n", 
              micro_sec, mili_sec, sec);

    printf("\nEnter unit of Time Period: ");

    period = getchar();

    if (period == micro_sec || period == mili_sec || period == sec) {
        printf("Enter Time Period: ");

        if (scanf("%d", &time) != 1) {
            printf("Error reading time!\n");
            exit(EXIT_FAILURE);
        }

        printf("\nUnit of time: %c\n", period);
        printf("Time Period: %d\n", time);

    } else {
        printf("\nIncorrect unit of time entered.\n");
    }

    return 0;
}

warning: array subscript is above array bounds [-Warray-bounds] in module

2 Answers2