Selecting random values of an array of strings in C

Question

I want to have an array of strings, and something return a random string from that array, so something like this:

 char* initialblow[] = {"hey", "hi", "hello"}; // this might be bigger or smaller
 char* secondblow[] = {"Bob", "Phil", "Sue"}; 
 int length1 = sizeof(initialblow)/sizeof(char); 
 int length2 = sizeof(secondblow)/sizeof(char);

 ...

 return initialblow[rand() % length1] + ", " + secondblow[rand() % length2]

Am I messing something really obvious up? I haven't touched C for a long time and can't figure out the issue.

Nick · Accepted Answer · 2014-03-05 11:40:54Z

3

Instead of

int length1 = sizeof(initialblow)/sizeof(char);

use

int length1 = sizeof(initialblow)/sizeof(*initialblow);

and instead of

return initialblow[rand() % length1] + ", " + secondblow[rand() % length2]

use something like

char out[256];
sprintf(out, "%s,%s", initialblow[rand() % length1], secondblow[rand() % length2]);

answered Mar 5, 2014 at 11:40

Nick

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2 Comments

Cassidy Over a year ago

Thanks @Nick! I just looked up sprintf() and just so I'm clear, does this mean that if I were to print out, it'd be the string I wanted?

Cassidy Over a year ago

@Nick I'm returning back to this, what if I want to return out? Would I have a function that's something like: char* getOut() { return *out; }, or something else?

hivert · Accepted Answer · 2014-03-05 11:54:27Z

3

Your computation of the length is wrong. initialblow is not an array of char but of char*:

int length1 = sizeof(initialblow)/sizeof(*initialblow);

Also, you can't concatenate string like this in C. You have to use strcat to concatenate a string into an existing one. For this either pass an extra char [] parameter and fill it with the result or do some dynamic allocation to return a char*.

edited Mar 5, 2014 at 11:54

answered Mar 5, 2014 at 11:39

hivert

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1 Comment

Graham Borland Over a year ago

I always find it easier to remember sizeof(initialblow)/sizeof(initialblow[0]).

legends2k · Accepted Answer · 2014-03-05 11:39:54Z

2

You can't initialblow[rand() % length1] + ", " + secondblow[rand() % length2] concatenate like this. What you're doing here is char + char* + char - which is illegal.

initialblow[rand() % length1] is a char

"," is a char*

secondblow[rand() % length2] is a char

If you really want to return a string, then make one (see Nick's answer). However, if you want to return it to the caller, instead of consuming it in the function then you've to go with dynamic memory allocation.

answered Mar 5, 2014 at 11:39

legends2k

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