CODEWITHSUNDEEP
cdata-structures
Kanad
Kanad

Reputation: 11

Read text from structure in c

struct Text{
       int length;
       char *txt;
};
void print(struct Text myTxt)
{
     while ( myTxt.txt < myTxt.txt + myTxt.length )
     {
           printf("%c", ++myTxt.txt);
     }
}
int main()
{
    struct Text myText;
    char test[] = "long long test text";

    myText.length = sizeof (test) / sizeof (char);
    myText.txt = test;

    print(myText);

    gets();
    return 0;
}

I know that print function is wrong, but how to fix it.

Upvotes: 1

Views: 149

Answers (5)

Tony Le
Tony Le

Reputation: 21

Try:

void print(struct Text myTxt)
{
     int i = 0;
     while (i < myTxt.length )
     {
           printf("%c", myTxt.txt[i]);
           i++;
     }
}

What you did wrong: you printed the addresses of each character, and incrementing it.

what mytxt.txt is doing is mytxt.txt = mytxt.txt + 1; therefore you are creating an infinite loop when you are checking the argument for the while loop.

Upvotes: 2

Node
Node

Reputation: 3509

If you need to support NULL bytes:

#include <ctype.h>
#include <stdio.h>
void print(struct Text *myTxt)
{
    int i;
    for (i = 0; i < myTxt->length; i++)
    {
        if (isprint(myTxt->txt[i]))
        {
            printf("%c", myTxt->txt[i]);
        }
        else
        {
            int num = (int)((unsigned char)myTxt->txt[i]);
            printf("\\%x", num);
        }
    }
}

If you don't:

#include <stdio.h>
void print(struct Text *myTxt)
{
    printf("%s", myTxt->txt);
}

Upvotes: 1

Regexident
Regexident

Reputation: 29552

This should be alright:

void print(struct Text myTxt) {
    printf("%s", myTxt.txt);
}

(This of course requires myTxt.txt to be null-terminated but for c string this is common anyway.)

So unless your string should be able to contain additional null bytes you could change your code to this:

struct Text{
       char *txt;
};
void print(struct Text myTxt)
{
    printf("%s", myTxt.txt);
}
int main()
{
    struct Text myText;
    myText.txt = "long long test text";
    print(myText);
    return 0;
}

You can get the string's length by calling
strlen(myTxt.txt);
which IIRC requires:
#include string.h

Upvotes: 2

icktoofay
icktoofay

Reputation: 129011

Your problem is print modifies the struct passed into it. Specifically, to print each character, you're incrementing myTxt.txt and then printing that. Your while loop is also incorrect: myTxt.txt < myTxt.txt + myTxt.length will always be true if myTxt.length is greater than zero.

You can fix it like this:

void print(struct Text myTxt)
{
     char *txt = myTxt.txt;
     while ( txt < myTxt.txt + myTxt.length )
     {
           printf("%c", *txt++);
     }
}

This sets txt to myTxt.txt, so you can modify txt without modifying myTxt.txt.

Upvotes: 3

Nemo
Nemo

Reputation: 71525

Assuming myTxt.length is greater than zero, myTxt.txt < myTxt.txt + myTxt.length is always true.

So your while loop never terminates.

[Edit]

Well, I suppose it terminates once the addition overflows an int. Still probably not what you intended.

Upvotes: 2

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