a simple question about about "scanf"

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#include "stdio.h"
void main()
{
	char a[20];
	scanf("%s",a);
	printf("%s",a);
}

I want to input less than 20 characters, how to control the number I input?
if the number is more than 20, the program should give me a warn, I want to know how to do this,Thank you.

Posted 14-Dec-12 0:29am

Angela2012

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4 solutions

Solution 4

C++

#include <stdio.h>
#include <string.h>

void main()
{
	char a[20];
        int i, c=1;
        while(c == 1)
        {
              if(strlen(a) > 19)
              {
                   printf("WARNING\n");
                   printf("DANGER FOR BUFFER OVERFLOW");
              }
              printf("Give the next char: ");
	      scanf("%s", &a[i]);
	      printf("Scanned char: %c\n",a[i]);
              printf("If you want to input another char type 1 or type another number to exit");
              scanf("%d", &c);
              i++;
        }
}

Posted 14-Dec-12 4:35am

Snk Tay

Updated 14-Dec-12 20:56pm

v2

Comments

Angela2012 14-Dec-12 19:53pm

Thank you very much,in your solution "strlen(a)" is always larger than 19

Snk Tay 15-Dec-12 5:11am

strlen(a) is not always larger than 19. Because the array a[20] is empty at the begining and the lefth of array getting bigger when you add a char.

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Jochen Arndt · Accepted Answer · 2012-12-14T00:50:00

With scanf() and strings, you should always pass the width to specify the max. number of chars to be stored (pass one less than the size of the char array to store the terminating NULL char). So with max. 20 chars use:

C++

char a[21];
scanf("%20s",a);

To get the number of chars entered, use the strlen() function afterwards. To show a warning when too much chars has been entered, allow one more character to be scanned and compare the final string length:

C++

char a[22];
scanf("%21s",a);
if (strlen(a) > 20)
{
    // show warning here
}

CPallini · Accepted Answer · 2012-12-14T00:48:00

Solution 1

You may use the width specifier (see the security note in the MSDN documentation[^]), e.g.

C++

scanf("%19s",a);

(and always check scanf result)

Posted 14-Dec-12 0:48am

CPallini

v2

Comments

Jochen Arndt 14-Dec-12 6:52am

+5. Beat me by a minute.

Angela2012 14-Dec-12 20:03pm

Thank you ,but I want to know if it is possible to check the number of characters automatically using scanf,when the number is larger than 20,it will give me a warn immediately rather than I finish inputting a very very long string.

CPallini 15-Dec-12 4:58am

No, it is not possible.

Mohibur Rashid 15-Dec-12 5:16am

it is not possible with scanf is true

Espen Harlinn 17-Dec-12 12:36pm

5'ed!

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ) · Accepted Answer · 2012-12-14T00:51:00

Solution 3

Please check Answer - How to limit scanf function in C to print error when input is too long?[^] and other answers too.

Thanks...

Posted 14-Dec-12 0:51am

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ)

Comments

CPallini 14-Dec-12 7:29am

5, even if you're advertising 'The Competitors' :-)

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ) 14-Dec-12 7:51am

Thanks a lot @CPallini.

a simple question about about "scanf"

4 solutions

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Solution 1

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