Print string from 2 dimensional character array

Question

I've looked around and tried different syntax's for this but I can't seem to get it to work. I know this is elementary, but it's something that shouldn't take too long to figure out.

I have the character array...

char *roster[2][14] = {
      {"13", "10", "24", "25", "15", "1", "00", "4", "11", "23", "22", "32", "3", "35"},
      {"Isaiah Briscoe", "Jonny David", "EJ Floreal", "Dominique Hawkins", "Isaac Humphries", "Skal Labissiere", "Marcus Lee", "Charles Matthews", "Mychal Mulder", "Jamal Murray", "Alex Poythress", "Dillon Pulliam", "Tyler Ulis", "Derrick Willis"}
    };

Then I'm generating a random element from that array...

random = rand() % 14;
printf("What is %s 's number?", roster[2][random]);

Then I try to print it out, but it fails...

printf("What is %s 's number?", roster[2][random]);

It outputs

What is (null) 's number?

and lldb shows that the printf statement jumps into...

libsystem_c.dylib`strlen:
->  0x7fff9a596d32 <+18>: pcmpeqb (%rdi), %xmm0
    0x7fff9a596d36 <+22>: pmovmskb %xmm0, %esi
    0x7fff9a596d3a <+26>: andq   $0xf, %rcx
    0x7fff9a596d3e <+30>: orq    $-0x1, %rax

random is a well known system function name, defined in stdlib.h. It is a bad idea to declare a variable name the same as a system function name. — user3629249
– user3629249, Commented Nov 14, 2015 at 16:23

Haris · Accepted Answer · 2015-11-13 16:03:19Z

2

Array index starts from 0.

For char *roster[2][14];, the possible indices are

roster[0][random];
roster[1][random];

answered Nov 13, 2015 at 16:03

Haris

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ergonaut · Accepted Answer · 2015-11-13 16:03:33Z

2

Arrays in c start at 0, so if you declare:

char *roster[2]

Then you can only reference roster[0] and roster[1].

answered Nov 13, 2015 at 16:03

ergonaut

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Comments

ameyCU · Accepted Answer · 2015-11-13 16:02:27Z

printf("What is %s 's number?", roster[2][random]);

You access index out of bound invoking undefined behaviour .

Because you can have indices roster[0][random] and roster[1][random] not roster[2][random] because it is declared as -

char *roster[2][14] = {
  {"13", "10", "24", "25", "15", "1", "00", "4", "11", "23", "22", "32", "3", "35"},
  {"Isaiah Briscoe", "Jonny David", "EJ Floreal", "Dominique Hawkins", "Isaac Humphries", "Skal Labissiere", "Marcus Lee", "Charles Matthews", "Mychal Mulder", "Jamal Murray", "Alex Poythress", "Dillon Pulliam", "Tyler Ulis", "Derrick Willis"}
};

You can print these -

printf("What is %s 's number?", roster[1][random]);

Or -

printf("What is %s 's number?", roster[0][random]);

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