C program to find substring in string

Question

So I may be attacking this the wrong way; I was learning a bit of Javascript and wrote a program that will find a string contained in another string and store the matches in an array (sorry if that didn't make too much sense, seeing my C program should help). I tried to translate my program to C, but it doesn't work; I think my issue is data types:

 int main () {
    char text[58];
    strcpy(text, "I am James, James the Great, a pretty cool guy named James"); 
    char store[16];
    char name[6] = "James";
    for (int i = 0; i <= 16; i++) {
        if (text[i] == 'J') {
            for (int k = i; k < i + 6; k++) {
                store[k] = text[i];
                }
        }
    }
    int a = sizeof(store) / sizeof(store[0]);
    for (int b = 0; b < a; b++) {
        /* This should print out the values stored in the store array */
        printf("%d", store[b]);
    }
    return 0;
}

My expected result would be something like:

JamesJamesJames

Instead I get:

10000747474747474-6374747474

So I'm assuming it's doing exactly what I told it to do, just not storing the letters into the array as letters, a bit confusing. Is there a better way to do this?

This is the javascript code I was trying to translate:

var text = "I am James, James the Great, a pretty cool guy named James";

var myName = "James";
var hits =[];
for (i = 0; i < text.length; i++) {
  if (text[i] === "J") {
      for (var j = i; j < i + myName.length ; j++) {
          hits.push(text[j]);
      }
  }
}
if (hits.length === 0) {
    console.log("Your name wasn't found!");
} else{
    console.log(hits);
}

is there some problem with simply using the system function: strstr() ? — user3629249
– user3629249, Commented Apr 5, 2015 at 20:44

Weather Vane · Accepted Answer · 2015-04-05 16:54:49Z

1

You are going to break store[] with this line

for (int k = i; k < i + 6; k++) {

because you are writing to the same index as you found the text in text[]. You also loop one too many times (6)

int ind = 0;
for (int k = 0; k < 5; k++) {
    store[ind++] = text[i+k];
}

Then your next statement doesn't tell you anything about the data you collected

int a = sizeof(store) / sizeof(store[0]);

Just remove it, and print ind characters from store[].

answered Apr 5, 2015 at 16:54

Weather Vane

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Comments

dagi12 · Accepted Answer · 2015-04-05 17:15:31Z

0

You made following mistakes.

for (int i = 0; i <= 16; i++)

You iterate by '16' but this isn't proper length of text.

for (int k = i; k < i + 6; k++)

So you iterate by "i, i+1, i+2, i+3, i+4, i+5, i+6" here is 7 chars, "James" have 6.

store[k] = text[i];

You aren't changing "i" value so text[i] always return 'J'. It's better to use savePoistion variable so do I in the following code.

int a = sizeof(store) / sizeof(store[0]);
    for (int b = 0; b < a; b++) {
        /* This should print out the values stored in the store array */
        printf("%d", store[b]);
    }

I have no idea what are you trying to do here. It's really unnecessary.

printf("%d", store[b]);

"%d" means that you are printing integers so don't be surprised that your output was numbers. Just simply printf("%s\n", store);

This should look like this

int main () {
    char text[58];
    strcpy(text, "I am James, James the Great, a pretty cool guy named James");
    char store[20];
    int len = strlen(text);
    int savePosition = 0;

    int i, k;
    for (i = 0; i < len; i++) {
        if (text[i] == 'J') {
            for ( k = i; k < i + 5; k++) {
                store[savePosition] = text[k];
                ++savePosition;
                }
        }
    }
    store[savePosition] = '\0';
    printf("%s\n", store);
    return 0;
}

edited Apr 5, 2015 at 17:15

answered Apr 5, 2015 at 17:00

dagi12

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1 Comment

steelcowboy Over a year ago

Yeah, I think I had it as %s earlier but it accidentally turned into a %d. Thank you very much, great answer and really easy to follow!

BLUEPIXY · Accepted Answer · 2015-04-05 17:23:33Z

0

int main (void) {
    char text[] = "I am James, James the Great, a pretty cool guy named James"; 
    char name[] = "James";
    char store[16] = {0};
    int store_index = 0;
    for (int i = 0; i < strlen(text); i++) {
        if (text[i] == 'J') {
            for (int k = i; k < i + strlen(name); k++) {
                store[store_index++] = text[k];
            }
        }
    }
    if(strlen(store)==0) {
        printf("Your name wasn't found!\n");
    } else {
        printf("%s\n", store);
    }
    return 0;
}

rewrite version.

int main (void) {
    char text[] = "I am James, James the Great, a pretty cool guy named James"; 
    char name[] = "James";
    char store[sizeof(text)];
    char *p = strstr(text, name);
    if(p == NULL) {
        printf("Your name wasn't found!\n");
    } else {
        int len = strlen(name);
        int index = 0;
        do {
            memcpy(store + index, name, len);
            index += len;
            p = strstr(p + len, name);
        } while(p != NULL);
        store[index] = 0;

        printf("%s\n", store);
    }
    return 0;
}

edited Apr 5, 2015 at 17:23

answered Apr 5, 2015 at 16:54

BLUEPIXY

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4 Comments

Weather Vane Over a year ago

just beat me with a better answer, but I suggest for (int i = 0; i <= strlen(text)-strlen(name); i++)

BLUEPIXY Over a year ago

@WeatherVane yes, this code has problem. but I was trying to translate javascript version.

steelcowboy Over a year ago

Great code, but a little hard to correlate with the javascript lol. But this definitely will help me get the feel of C a little better, thanks!

BLUEPIXY Over a year ago

@steelcowboy dagi12's code has same problem that Weather Vane has been pointed out by his comment.

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