help with strings in C

Question

I'm studying for an exam and I need some help with strings

Assume the following declarations, and further assume that string.h is uncluded

char rocky[21], bw[21], boris[21];
int result;

a.) Write a scanf statement that would enable the string Beauregard to be read into rocky

my answer= scanf("%s", &rocky);

b.) Assuming that the text Beauregard is the only thing on th eline of standard input, write a statement to read in the text and store it in rocky using an alternative to scanf

my answer= gets (Beauregard); strcpy(rocky);

c.) assuming that the text read in is Beauregard, what is the value of result after the following statement is executed?

result=strlen(rocky);

my answer= i have no clue..

d.) what does the following statment do?

strcpy(boris, rocky);

answer= makes a copy of the string..(dont know much more than that)

e.) what does the following statement do? What are the values of rocky and bw?

strncpy(bw,rocky,3);

my answer= not a clue

help is much appreciated, and an explanation would also help :)

Thanks!

Reading the documentation of the functions is usually helpful.. — Demian Brecht
– Demian Brecht, Commented May 3, 2011 at 1:53
Why don't you try putting these into (a) program(s), compiling, and testing? — GreenMatt
– GreenMatt, Commented May 3, 2011 at 1:56
Why do schools insist on teaching those functions? scanf and gets are both dangerous: en.wikipedia.org/wiki/Gets, en.wikipedia.org/wiki/Scanf#Security — Brendan Long
– Brendan Long, Commented May 3, 2011 at 2:01

deong · Accepted Answer · 2011-05-03 02:02:03Z

a. Arrays and pointers are closely related in C. In particular, the name of an array decays to a pointer to the first element of the array, so your answer should be

scanf("%s", rocky); /* note the lack of an & in front of rocky */

b. gets(Beauregard) doesn't really make sense. The gets function reads a string from standard input (think, "keyboard") and stores it in the character array pointed to by the argument you pass it. So you're supposed to assume the user will type "Beauregard", and you should read it into the rocky array with

gets(rocky);

c. strlen returns the length of the string, not including the trailing \0 character, so in this case, 10.

d. strcpy just copies the contents of the rocky array into the boris array, so they'd both contain "Beauregard".

e. strncpy works like strcpy, but only copies up to n characters (where n is the last argument, so in this case, bw would contain "Bea" without a terminating null character.

Note that several of these statements are really bad ideas in any real program. There is never a reason to use gets, for example, as any use of gets opens up security flaws. You should always use fgets instead. The scanf function can be used safely if you specify the width, but you haven't done so here. I mention these things just in case your teacher has covered them and you've forgotten.

Seth Carnegie · Accepted Answer · 2011-05-03 01:56:46Z

1

strlen returns the length of the C string. strlen("Beauregard"); would return 10 because the string is 10 characters long.

strcpy just copies a string, you're right.

strncpy allows you to specify the maximum number of characters you want. So if you pass it 3, you'll get 3 characters and the null terminator on the end of your string.

answered May 3, 2011 at 1:56

Seth Carnegie

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Comments

vpit3833 · Accepted Answer · 2011-05-03 02:00:38Z

0

strlen(rocky) is going to return the string length of what is pointed to by rocky. The number of letters that make up 'Beauregard'.

strncpy(bw, rocky, 3) copies the first 3 letters from the string pointed to by rocky into bw.

You should read man pages for strlen, strcpy and strncpy.

answered May 3, 2011 at 2:00

vpit3833

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Cory G. · Accepted Answer · 2011-05-03 02:01:08Z

0

c.) strlen counts until it reaches the terminating null character, \0. So the answer would be 10, because there are 10 letters in Beauregard. Strlen

d.) Yes, it copies a string. More specifically, it copies rocky into boris. I'm not sure what else they would want you to give as part of an answer there...

e) It copies the first 3 characters of rocky into bw. However, it does NOT add a terminating null character. strncpy

answered May 3, 2011 at 2:01

Cory G.

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