when retrieving an array element, how can I use a variable as the element number

Question

I am working on some code to parse log data, this part in particular is used to translate the decimal form of a month to a human form ( so 1 would be jan ), and to accomplish this I am trying to use a combination of a for loop and an if statement, and had thought that I could simply use a variable as the number for the statement to retrieve the array cell, but it did not work out as expected, so if someone could offer advice as to how I can do this I would really appreciate it, thanks! (here is the main chunk of the code)

for ( x = 0; x < 11; x++ ) {
    int altint = 1 + x;
    if ( dmon == altint ) {
            printf( "%s\n", field_month[x] );
            {break;}
    }
}

field month is an array with the human names of the months, so { jan, feb, march, etc } and then dmon is the decimal version of the month — lacrosse1991
– lacrosse1991, Commented May 17, 2012 at 0:44
oh shit actually had made a dumb mistake, had mixed up the name of the array itself and the numerical reference to the month, works perfectly now though, thanks! — lacrosse1991
– lacrosse1991, Commented May 17, 2012 at 0:51

sarnold · Accepted Answer · 2012-05-17 00:44:36Z

2

I'd like to suggest that you not use a for loop and instead look up the element that you want directly:

printf("%s\n", field_month[dmon]);

If your dmon is 1-indexed (1 for January, .., 12 for December), then a slight change:

printf("%s\n", field_month[dmon-1]);

answered May 17, 2012 at 0:44

sarnold

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7 Comments

sarnold Over a year ago

@Evan, note that tpaksu updated his answer to include dmon-1.

Evan Mulawski Over a year ago

True, but your explanation is clear and concise. I updated my comment.

lacrosse1991 Over a year ago

thanks! and if I wanted to save the output would I just save the output of printf to a variable?

sarnold Over a year ago

@lacrosse1991: You'd have trouble saving the output of printf(3) to a variable -- it, after all, prints to a standard IO stream. Probably better would be something like char *month = field_month[dmon];. (That gives you a pointer to the data -- it doesn't make a copy of it. That will be important later. :)

lacrosse1991 Over a year ago

thanks! worked perfectly as well, sorry if those were dumb questions, still getting the hang of things, the speed at which C operates at though is well worth it :)

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Taha Paksu · Accepted Answer · 2012-05-17 00:43:58Z

2

just printf("%s",field_month[dmon]) or field_month[dmon-1] as it depends on your month names array?

answered May 17, 2012 at 0:43

Taha Paksu

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Comments

Thomas C. G. de Vilhena · Accepted Answer · 2012-05-17 00:50:19Z

0

Your for loop can be optmized to:

if (dmon >= 1 && dmon <= 12)
{
    printf("%s\n", field_month[dmon]);
}

Because the only thing it's really doing is preventing an invalid index of being used to access your array...

answered May 17, 2012 at 0:50

Thomas C. G. de Vilhena

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1 Comment

sarnold Over a year ago

Good point about avoiding bad array accesses -- but arrays are zero-based and thus indexed from 0 to 11 -- unless a bogus element is stored in the first array position.

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