Function to search for string in array of strings

Question

I am trying to write a function that searches for the unique part(maximum two characters) of a string in an array of strings. Although strstr and strchr are not working and crash my program for some reason. So I have resorted to trying to create something that resembles their function.

My question is this:
Why is strstr not working (something like strstr(lex[j],word)) and what am I doing wrong here?

Here is the code for the function that searches for two unique characters within an array of strings :

void convert(char word[])
{
    int i;

    for (i = 0 ; i <= strlen(word) ; i++)
    {
        if(word[i] >= 65 && word[i] <= 90)
        {
            word[i] = word[i]+32;
        }
    }
}


int  twochar(char lex[50][50],char word[], int size,char temp[3])
{
    int i,j,k,count,totlen;
    convert(word);

    for (i = 0 ; i < strlen(word) - 1 ; i++)
    {
        count = 0;
        totlen = 0;
        for(j = 0; j<size; j++)
        {
            convert(lex[j]);
            totlen += strlen(lex[j]) - 1;
            for(k = 0 ; k < strlen(lex[j]) - 1 ; k++)
            {
                if (word[i] != lex[j][k] || word[i+1] != lex[j][k + 1])
                {
                    count++;
                }
            }
        }
        if(count =  = totlen)
        {
            temp[0] = word[i];
            temp[1] = word[i+1];
        }
    }
}



int main(int argc, char *argv[])
{
    char lex[50][50] =  {"word1","word2","word3","word4" }, word[] = "test";
    char p[3];

    twochar(lex,word,4,p);
    printf("%c%c\n",p[0],p[1]);
    return 0;
}

This strlen(lex[j])-1 is a receipe for desaster. Imagine what happens if lex[j] is an emtpy "string" with the length of 0. Hint: Check the type strlen() returns. — alk
– alk, Commented Apr 22, 2015 at 16:55
I deleted my comment which said you do not terminate temp[] by using temp[2]='\0' because I noticed you never use temp or p as a string, only as a plain array. — Weather Vane
– Weather Vane, Commented Apr 22, 2015 at 16:57
well i know it's not the best solution, but what could be an alternative? — Shivalnu
– Shivalnu, Commented Apr 22, 2015 at 16:57
Run your code in a debugger, trace through it and inspect the relevant values. To learn how to do this you might like to read here: ericlippert.com/2014/03/05/how-to-debug-small-programs — alk
– alk, Commented Apr 22, 2015 at 17:00
In that case the code would be clearer as if(word[i] >= 'A' && word[i] <= 'Z') — Weather Vane
– Weather Vane, Commented Apr 22, 2015 at 17:07

user3629249 · Accepted Answer · 2015-04-22 17:58:05Z

2

this line:

for(k=0;k<strlen(lex[j])-1;k++)

is the problem.

strlen(lex[0]) is 0
strlen(lex[0])-1 is -1 (0xFFFFFFFF in a 32 bit system)
k starts at 0 and is incremented until it is equal to 0xFFFFFFFF

of course, k exceeds the bounds of lex[0] when k = 50.

the result is undefined behaviour which leads to the seg fault event

To determine all the above, I compiled/linked the program via gcc, with the -ggdb parameter.

then I ran the program via 'gdb theprogram'

within gdb I entered
br main <-- break point set
run
c <-- continue
the program then crashed with a seg fault event
then I entered
bt  <-- back trace
the bt showed me this line: 'if(word[i]!=lex[j][k] || word[i+1]!=lex[j] [k+1])'
Then I entered
p k <-- print variable k
=6832   (which is WAY out of bounds)

then I entered
run
y
br theprogram.c:41    (the line number from above) <-- set another break epoint
c
the program stopped at line 41
p j
=0  ( this was the gdb response )
p k 
= 0
p i
= 0

a little thinking, 
stepping though that inner loop using 'n' <-- next
and playing on gdb 
indicated that the problem was in line 42
and resulted in revealing the root of the problem

edited Apr 22, 2015 at 17:58

answered Apr 22, 2015 at 17:49

user3629249

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1 Comment

user3629249 Over a year ago

BTW: the compiler warnings can be eliminated by declaring certain of the loop variables as 'size_t' rather than 'int'

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