scanning in character string

This is a discussion on scanning in character string within the C Programming forums, part of the General Programming Boards category; I have a question in regards to scanning in a character array with spaces for a project im working on ...

  1. #1
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    scanning in character string

    I have a question in regards to scanning in a character array with spaces for a project im working on for an introductory class in C programming.

    I know that I cant use the scanf function becasue it will stop scanning in the characters once it sees a space. Our teacher told us to use the "gets" function.

    The string can have a maxium length of 50 characters. So I defined the string variable as
    char str[51];
    to leave an extra space for the the \0

    I can get the gets function to work in an easy case

    Code:
    char str[51];
    printf("Enter the string:");
    gets(str);

    it works fine for this. This is probally a dumb question, but will the gets function be skipped, if it is inside a loop. My program just seems to skip right over the gets function, but if I replace it with a scanf function everything works fine(except for the fact that I cant scan in more than one word).

    Here is the basic structure of the part of the program that I am having trouble with.

    Code:
    #include<stdio.h>
    #define SIZE 50
    
    int selection(void);  //prototype of function that chooses encryption method
    
    int main()
    {
      int choice=0;
      char str[SIZE];
    
      while(choice!=5)
      {
        choice=selection();
        printf("Enter the string now: ");
        gets(str);
      }
    return(0);
    }
    
    
    int selection(void)
    {
      int choice;
      int lcv=1;
    
      printf("Chose method 1-5 by entering integer, ect.")
      while(lcv==1)
      {
        scanf("%d",&choice);
        if(//input validation)
        {
           correct while loop while quit
        }
        else
        {
          while loop will continue
        }
      }
    return(choice);
    }

    In this case, the program doesnt stop and give the user a chance to input a string like it did in the first example.

    any help would be appreciated
    thanks,
    Zack

  2. #2
    Obsessed with C chrismiceli's Avatar
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    http://faq.cprogramming.com/cgi-bin/...&id=1043284351
    Also, the reason that gets is being skipped is because it is picking up the newline character left on the screen by scanf(), Don't use gets, but if you use scanf(), keep in mind that it leaves the enter on the buffer, waiting for some input function to grab it.
    Last edited by chrismiceli; 11-23-2004 at 12:46 AM.
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  3. #3
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    so I should use fgets?

    would this be better, replace the

    Code:
    gets(str);
    with

    Code:
    fgets(str, SIZE, stdin);
    I am also not sure what stdin is for. Thanks for the help

    Zack

  4. #4
    and the hat of int overfl Salem's Avatar
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    Code:
    FILE *fp = fopen( "file.txt", "r" );
    fgets( buff, sizeof buff, fp );
    stdin is just the predefined variable of type FILE* which is attached to the standard input stream of your program.

    Similarly,
    Code:
    scanf( "%d", &myint );
    fscanf( stdin, "%d", &myint );
    are the same thing.

    To avoid all the problems which scanf has with leaving newlines (and generally poor error recovery in general), just use fgets() to read a line, then use sscanf() to parse the line.

  5. #5
    ATH0 quzah's Avatar
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    Quote Originally Posted by zackboll
    would this be better, replace the

    Code:
    gets(str);
    with

    Code:
    fgets(str, SIZE, stdin);
    Sure, it'd be better. Unless you're Mister C.

    Quzah.
    Hope is the first step on the road to disappointment.

  6. #6
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    Quote Originally Posted by Salem
    To avoid all the problems which scanf has with leaving newlines
    Code:
    scanf("%d\n");
    Solved


    To flush the input buffer you may use.
    Code:
     
    void FlushInput(){
        char c;
        do{
            c=getchar();
        }while( c!= '\n' && c!= EOF);
    }
    Disadvantage: if there's nothing in the input buffer you'll have to write something to it. But there's an alternative, although not very popular.

  7. #7
    and the hat of int overfl Salem's Avatar
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    > scanf("%d\n");
    Nope - that just creates a different set of problems

    Your FlushInput() also declares c as char, whereas it should be int if you want to meaningfully compare with EOF

  8. #8
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by xErath
    Code:
    scanf("%d\n");
    Solved
    www.eskimo.com/~scs/C-faq/q12.17.html
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  9. #9
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    So stdin is referring to the input buffer. I am not reading the string from a file, but rather the user types it in.

    will I have to flush the buffer after the user goes through the "scanf" for a single integer input, but before going through the "fgets". I know that fflush(stdin) is bad from various members of the board, as well as the faq, but for some reason, that is what our teacher tells us to do. I was having a problem before with the "gets" function being skipped becasue it would read in a newline from the "scanf" function. If I somehow cleared the buffer after my "scanf" statement, and used "fgets" instead of "gets", would my problem be solved?

    thanks for the help,
    Zack


    Quote Originally Posted by Salem
    Code:
    FILE *fp = fopen( "file.txt", "r" );
    fgets( buff, sizeof buff, fp );
    stdin is just the predefined variable of type FILE* which is attached to the standard input stream of your program.

    Similarly,
    Code:
    scanf( "%d", &myint );
    fscanf( stdin, "%d", &myint );
    are the same thing.

    To avoid all the problems which scanf has with leaving newlines (and generally poor error recovery in general), just use fgets() to read a line, then use sscanf() to parse the line.

  10. #10
    Just Lurking Dave_Sinkula's Avatar
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    FAQ > How do I... (Level 1) > Get a line of text from the user/keyboard (C)
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  11. #11
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    Quote Originally Posted by Dave_Sinkula
    Hum... still it did work many times with me... Ok then, no newline!

  12. #12
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    thanks

    thanks for link

    Quote Originally Posted by Dave_Sinkula
    FAQ > How do I... (Level 1) > Get a line of text from the user/keyboard (C)

  13. #13
    and the hat of int overfl Salem's Avatar
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    > Hum... still it did work many times with me
    Yeah, "works for me" is a continual hazard

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