I used calloc to clear the string hear. is it a good idea?

**sagar474** · 09-15-2011

Code:

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define length(x) strlen(x)
int main(int argc,char* argv[])
{
    char *string;
    string=(char *)malloc(20);
    register char special;
    register    short int i=0,a=0;
    register    short int c;

    FILE *fp;
    fp=fopen(argv[1],"r");

    while(1)
    {
        while(!feof(fp))
        {
            a=0;
            string=(char *)calloc(20,1);//<<========<<Hear


            while(!feof(fp))//
            {
                c=getc(fp);
                special=c;
                if((c>=65 && c<=122))
                {
                    string[a]=c;

                }
                else if(c>=48 && c<=57)
                {
                    string[a]=c;

                }
                else break;

                ++a;
            }

            i=length(string)-1;
            while(i>=0)
            {
                putchar(string[i]);
                --i;
            }
            if(c=='\n')break;
            if((c>=0 && c<=126))
                putchar(special);
        }
        if(c==EOF)break;
        putchar('\n');
    }
    fclose(fp);
    return 0;
}

I calloc, malloc and realloc are used for dynamic memory allocation but I do not need any dynamic memory allocation in this program. is there any other way to avoid dynamic memory allocation and hence speed up the program ?

**quzah** · 09-15-2011

Just use an array if you don't need dynamic allocation.

Quzah.

**sagar474** · 09-15-2011

Originally Posted by quzah

Just use an array if you don't need dynamic allocation.

but I have to clear the string at line indicated by "//<<=======<<" in the code each time I execute the loop .

**quzah** · 09-15-2011

So do like I showed you in the other thread, and use a loop. Or use something like memset, but at this point you should probably learn how to do it manually with a loop. Once you are comfortable with that, switch it out for memset so you know how that works.

Quzah.

**Salem** · 09-15-2011

Well you should certainly read the FAQ on why using feof() to control a loop is bad.

Also, you have a massive memory leak, each calloc needs a free(), and you have none.

Third, it's also comparatively expensive to clear ALL the bytes of a string when all you really need to do is
string[a] = '\0';
when you're done.

You should also drop the use of 'register' and using #define to rename functions.
You're never going to guess correctly what is best to put in a register any better than an optimising compiler.

**sagar474** · 09-15-2011

Originally Posted by Salem

You're never going to guess correctly what is best to put in a register any better than an optimising compiler.

why shoudent i use register keyword ? I used them to store counter variables and a single char. where should I use it ?

to clear the string with this I need to write a loop.
string[a] = '\0';

**Salem** · 09-15-2011

40 years ago when there was only one C compiler in the world, and it didn't do much apart from actual literal compiling, "register" was an easy optimisation hint.

Now scroll forward to today.
Optimize Options - Using the GNU Compiler Collection (GCC)
There are so many things a modern compiler can detect and improve that random programmer guesses don't really come into it.
What is more, this happens EVERY time you compile, not whenever you feel the need to look at your code in detail.

Your use of "register" is at best a static guess. You're certainly not going to be sitting staring at the code for hours every time you make a change to decide whether your use of "register" is the best possible. For a start, you don't even know how many registers are available on your machine - if you have only 2 registers, then putting "register" on 3 variables creates a bit of a problem - no?

**sagar474** · 09-15-2011

Thank you I fixed the problem of clearing the string. there is no need to clear a string in my program at all. instead of clearing a string i just used variable a to track the size of string.

but as suggested by salem feof is not a good idea to test the loop. Instead how can I terminate the loop in order to replace feof can i use c!=EOF ?

**AndrewHunter** · 09-15-2011

Originally Posted by sagar474

but as suggested by salem feof is not a good idea to test the loop. Instead how can I terminate the loop in order to replace feof can i use c!=EOF ?

Read: Why feof() is bad-FAQ, in there it shows the correct way to do this.

**quzah** · 09-15-2011

Originally Posted by sagar474

Thank you I fixed the problem of clearing the string. there is no need to clear a string in my program at all. instead of clearing a string i just used variable a to track the size of string.

Yeah you were told that in your first thread too: make a string empty in C

Quzah.

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