unexpected sign in fprintf, fscanf

Question

I received data to stream using scanf() and sent it to client.txt using fprintf():

#include <stdio.h>
#include <stdlib.h>

int main()
{
    system("clear");
    int servicestart;
    char tmp1[100], tmp2[100], tmp3[100], tmp4[100], tmp5[100];

    puts(">>Library Service<<\n1.Register 2.Log in 3.Exit Program");
    scanf("%d", &servicestart);

    switch (servicestart)
    {
    case 1:
    {
        system("clear");
        FILE* fp1 = fopen("client.txt", "w");

        if (fp1 == NULL)
        {
            puts("Write Error!!");
            return 0;
        }

        puts("You selected Register");
        puts("Enter Student ID | Password | Name | Address | Phonenumber");
        puts("ex)2018|ssu|DanielHong|Gaepo-dong|01031414473");
        printf("\n\n");

        scanf("%s|%s|%s|%s|%s", tmp1, tmp2, tmp3, tmp4, tmp5);
        fprintf(fp1, "%s %s %s %s %s", tmp1, tmp2, tmp3, tmp4, tmp5);
        fclose(fp1);
    }

    return 0;
}

However, when I entered 2018|asdf1234|danielhong|gaepo-dong|01023232323

there was 2018|asdf1234|danielhong|gaepo-dong|01023232323 p \ �� in client.txt.

I didn't enter p \ �� clearly.

I was in agony about it but don't having any clue about solution.

Can somebody help me for this problem?

If you mean client.txt , I created it in advance in home directory. — , Nov 27 '18 at 01:45
you could find out what the byte values for those pesky characters are using a hex viewer. Also what happens when you make this change: `fopen("client.txt","w+");` (Note the plus sign) — HappyKeyboard, Nov 27 '18 at 01:48
I solved the problem from the question below , but I`m curious about what is p \ �� too. I got 20 70 03 20 5C 03 20 A0 CB FF FF form hex viewer, — , Nov 27 '18 at 02:01
@DanielHong Thats just random data from `tmp2` - `tmp5` that got written without being initialized before. If you had initialized your arrays (`char tmp1[100] = { 0 }, tmp2[100] = { 0 }, tmp3[100] = { 0 }, tmp4[100] = { 0 }, tmp5[100] = { 0 };`) you wouldn't have seen that garbage. — Swordfish, Nov 27 '18 at 02:15
I was curious to see if there would be any new line feed or carriage return or line feed characters (you can look up ASCII Table to see what the values area) — HappyKeyboard, Nov 27 '18 at 02:20

score 3 · Accepted Answer · edited Nov 27 '18 at 01:57

The format specifier "%s" reads until the next whitespace. The next whitespace in your input is the newline ('\n') at the end of the line. Use

scanf("%99[^|]|%99[^|]|%99[^|]|%99[^|]|%99s", tmp1, tmp2, tmp3, tmp4, tmp5);

Instead. %[] is a scanset that matches all characters in the brackets. If the characters are prepended with a ^ they are excluded.

Please, never use "%s" or a scanset without specifying a width for the conversion specifier to limit the characters maximal read. Since your arrays are 100 chars long specify 99 so there is space left for the terminating '\0' character.

You should also check, if scanf was successful before proceeding to process the input. scanf() returns the number of conversions successfully performed. So in your case you schould compare the return value with 5:

if (scanf("%99[^|]|%99[^|]|%99[^|]|%99[^|]|%99s", tmp1, tmp2, tmp3, tmp4, tmp5) != 5) {
    ; // handle error
}

I'm truly greateful for excellent answer for my first question. thx — , Nov 27 '18 at 02:11

unexpected sign in fprintf, fscanf

1 Answers1