scanf doesn't input space as a character

Question

The program below is supposed to print out all the characters of a line from a file between two entered characters. It works fine for all test cases except for the one where one of the explicitly entered characters is a space.

ex.

Input:

12345 Maja Majovska: 54

15145 Aco Acoski: 95

14785 Martin Martinoski: 87

#

: //Under the hashtag is the space

Correct output:

Maja Majovska

Aco Acoski

Martin Martinoski

My output:

54

15145 Aco Acoski 95

14785 Martin Martinoski 87

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

void wtf() {
    FILE *f = fopen("podatoci.txt", "w");
    char c;
    while((c = getchar()) != '#') {
        fputc(c, f);
    }
    fclose(f);
}

int main()
{
    wtf();
    getchar();
    char z1, z2, c;
    FILE *f;
    f=fopen("podatoci.txt", "r");
    int flag=0;
    scanf(" %c %c", &z1, &z2);
    while((c=fgetc(f))!=EOF){
        if(c==z1){
            flag=1;
            continue;
        }
        if(c==z2){
            flag=0;
            printf("\n");
        }
        if(flag)
            printf("%c", c);
    }
    fclose(f);
    return 0;
}

Can someone point out simply what am i doing wrong? I'm new to working with files.

@PauseUnpause I don't get how I should reproduce the output you get. What exactly should I input? — gsamaras, Jan 13 '19 at 11:13
So it looks like you're assuming that you can both skip spaces and input spaces in a `' %c'` combination. Can you explain how the system is supposed to know which spaces to skip and which spaces to input? — n. m. could be an AI, Jan 13 '19 at 11:20
@gsamaras copy and paste everything before the hashtag. Hit enter and after every character after that hit enter. You'll get my output. — ptushev, Jan 13 '19 at 11:21
@n.m. I don't know. I thought leaving a space before the `%` is good practice in c — ptushev, Jan 13 '19 at 11:23
Leaving a space before the % has a very specific narrow purpose. — n. m. could be an AI, Jan 13 '19 at 11:28
The space directs `scanf` to skip all whitespace and stop right before a non-whitespace character. If you are planning to input a character that could possibly be a space with `%c`, then obviously skipping all spaces right before that is not what you want to do. — n. m. could be an AI, Jan 13 '19 at 11:34

Stef1611 · Answer 1 · 2019-01-13T13:26:02.473

I think this code should work. Enter the two characters at the same time #: (# is space) followed by enter

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

void wtf() {
    FILE *f = fopen("podatoci.txt", "w");
    char c;
    while((c = getchar()) != '#') {
        fputc(c, f);
    }
    fclose(f);
}

int main()
{
//    wtf();
//    getchar();
    char z1, z2, c;
    FILE *f;
    f=fopen("podatoci.txt", "r");
    int flag=0;
    printf("enter chars : ");
//    scanf(" %c %c", &z1, &z2);
//   printf("chars are |%c| |%c|",z1,z2);
    char name[3];
    fgets(name, 3, stdin);
//    printf("chars are |%c| |%c|",name[0],name[1]);
    char buffer[512]; // I suppose 512 is enough (see Two problems below)
    int i=0;
    while((c=fgetc(f))!=EOF){
/* Different problems :
    1 : you have a 'space' followed by 'end of line' before ':'
    example you have a space before 54 but end of line before :
    So you could not display characters when a 'space' is a found.
    You have to use a temporary buffer
    2 : you have to reset your flag at the end of line
    3 : If you have ':' alone, do not printf("\n")
    4 : If you have a 'space' after the first 'space', it must be printed
    example : Maja Majovska
                  ^ (this space)

*/
        if(c=='\n') { // Address pb 2
            flag=0;
            i=0;
            continue;
        }
        if(!flag&&c==name[0]){ // Address pb 4
            flag=1;
            continue;
        }
        if(flag&&c==name[1]){ // Address pb 3
            flag=0;
            buffer[i]='\0'; // end of string
            printf("%s\n",buffer);
            i=0;
        }
        if(flag)
            buffer[i++]=c; // Address pb 1
    }
    fclose(f);
    return 0;
}

Some remarks :

Most of the explanations are in the code comments (you could remove it after reading)

I use fgets instead of scanf (https://stackoverflow.com/a/1248017/7462275)

I do it like that to keep the code as close to its original form as possible. But, I think it would be better to get text line by line and use string functions (string.h). For example, to print the first substring between two characters (no sanity checks done : these two characters must be in the string)

while((fgets(buffer,512,f))!=NULL){
        i=strchr(buffer,name[0]);
        *(strchr(i,name[1]))='\0';
        printf("%s\n",i);
}

scanf doesn't input space as a character

1 Answers1