Print Certain Line in C

This is a discussion on Print Certain Line in C within the C Programming forums, part of the General Programming Boards category; Code: #include<stdio.h> struct student{ int id; char name[30]; int mark; }; void main() { FILE*fp; struct student stud; int id_no; ...

  1. #1
    Registered User
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    Nov 2007
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    Print Certain Line in C

    Code:
    #include<stdio.h>
    
    struct student{
    	int id;
    	char name[30];
    	int mark;
    };
    
    void main()
    {
    FILE*fp;
    
    struct student stud;
    int id_no;
    fp=fopen("data.txt","r);
    
    
    printf("enter id no : ");
    scanf("%d",&id_no);
    
    while(fscanf(fp,"%d %s %d",stud.id,stud.name,stud.mark)!=EOF)
    {
    
    if(id_no == stud.id)
    printf("%d %[^\n] %d\n",id_no,stud.name,stud.mark);
    
    else
    
    printf("Error !\n");
    
    }
    fclose(fp);
    
    }
    Hello Everyone,I am stuck at the middle how to print out the certain line from the the text file..for instance when the user enter id_no 12222 ,it should print out 12222 John Brown 80

    Data.txt
    22333 Smith Alison 70
    12222 John Brown 80
    12345 Chris Ratcel 60

    anyone plz help ...thx

  2. #2
    Kernel hacker
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    What result are you getting, and how is that different from what you expect?

    --
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  3. #3
    CSharpener vart's Avatar
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    &#37;s in scanf reads till the first white space encountered so stud.name will be
    "John" not "John Brown"

    use return value of scanf to see how many formats were parsed successfully

    with the file structure presented you need to read firstName and lastName into 2 different buffers
    you cannot read them together

    to avoid problems after failed parsing - better use pair fgets/sscanf instead of fscanf
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  4. #4
    and the hat of wrongness Salem's Avatar
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    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  5. #5
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    Hello there!

    I'm having difficulties with understanding what's happening with scanf() in combination with character formatter -&#37;c.

    Let's look at simple example:

    Code:
    #include <stdio.h>
    int main(void)
    {
      
      char c;
    
      scanf("%c",&c);
      scanf("%c",&c);
    
      system("PAUSE");	
      return 0;
    }
    Firstly printf() parses all newly typed data, so if I press character 'p' and then enter, the data would be: 'p','\n'.Since I provided character formatter, I'd expect that first character is taken and all additional are removed, but it seems they aren't.Now the interesting part; the 'p' seems to get assigned to variable c and new line-'\n' character is sent to input and waits to be parsed and that happens in second scanf() call.

    So what's the problem?Some guys told me that I have to supply a '\n' char in first argument.

    Code:
     scanf("%c\n",&c);
    Thing worked, but the question is why it worked?From here I can see only a new character added, which should create a new input information(one more loop), but no.Looks like this '\n' character in this context serves as "ignore \n data coming from input" or smth?

    And yes, I could use getstr(), but I'm kind of "Always the hard way" guy...

  6. #6
    Jack of many languages Dino's Avatar
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    Quote Originally Posted by W1ck3D View Post
    Hello there!

    I'm having difficulties with understanding what's happening with scanf() in combination with character formatter -%c.

    Let's look at simple example:

    Code:
    #include <stdio.h>
    int main(void)
    {
      
      char c;
    
      scanf("%c",&c);
      scanf("%c",&c);
    
      system("PAUSE");	
      return 0;
    }
    Firstly printf() parses all newly typed data, so if I press character 'p' and then enter, the data would be: 'p','\n'.Since I provided character formatter, I'd expect that first character is taken and all additional are removed, but it seems they aren't.Now the interesting part; the 'p' seems to get assigned to variable c and new line-'\n' character is sent to input and waits to be parsed and that happens in second scanf() call.

    So what's the problem?Some guys told me that I have to supply a '\n' char in first argument.

    Code:
     scanf("%c\n",&c);
    Thing worked, but the question is why it worked?From here I can see only a new character added, which should create a new input information(one more loop), but no.Looks like this '\n' character in this context serves as "ignore \n data coming from input" or smth?

    And yes, I could use getstr(), but I'm kind of "Always the hard way" guy...
    You have dug and figured out exactly how scanf() works. Good job. And yes, that's that way it works, just like the Sun rises in the East and sets in the West.
    Mac and Windows cross platform programmer. Ruby lover.

    Quote of the Day
    12/20: Mario F.:I never was, am not, and never will be, one to shut up in the face of something I think is fundamentally wrong.

    Amen brother!

  7. #7
    Registered User gavra's Avatar
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    All you need is to create a function that has 3 arguments: pointer to file, string to search, size of string then you should search for the string in your text file (if you ask "how?" the answer will be "think").
    goodluck
    gavra.

  8. #8
    Banned master5001's Avatar
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    Sometimes I wonder about you, Salem. You are like the the world-wide-stalker (and I mean it in the most endearing way possible).

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