fgets help

This is a discussion on fgets help within the C Programming forums, part of the General Programming Boards category; I'm making a program that has to read in and manipulate a pgm file. I need to make sure the ...

  1. #1
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    fgets help

    I'm making a program that has to read in and manipulate a pgm file. I need to make sure the first line in the file is P2, not P5. How would i go about doing this?

    so far i have something like this:

    Code:
    int continue;
    FILE *in;
    char buffer[MAXSIZE];
    
    in = fopen(image.pgm, "r");
    
    fgets(buffer, MAXSIZE, in);
    
    if( buffer[1] != 2 )
    {
        printf("Incorrect data type.\n");
        exit(0);
    }
    When i print out buffer[1] i get some big ass number. What am i doing wrong?

  2. #2
    cwr
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    You want to compare the character '2', not the numeric value 2. The value '2' in ASCII for example is 50.
    Code:
    if (buffer[1] != '2')
    Also, your filename needs to be in quotes.

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    Quote Originally Posted by cwr
    You want to compare the character '2', not the numeric value 2. The value '2' in ASCII for example is 50.
    Code:
    if (buffer[1] != '2')
    Also, your filename needs to be in quotes.
    ahh thanks. And i know about the file name, I actually have a variable there, but changed it just so it was easier to interpret...just forgot the quotes when i changed it

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    second question. I'm reading a line such as this:

    Code:
    200 100
    how would i go about setting the first number to the image height and the next to the width?

    I know this isn't right....at all, I'm just having a brain fart b/c its late, and I'm posting some code for you to work with. Its something along the lines of:

    Code:
                i=0;
                while(!isspace(buffer[i]))
                {
                    image.width = buffer;
                    i++;
                    if(isspace(buffer[i]))
                    {
                        break;
                    }
                }
    then just do the another one for the height. But how would i go about setting buffer[0] buffer[1] and buffer[2] to image.width?

  5. #5
    cwr
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    Your input is formatted as two integers, so why don't you read it in with fgets, then use sscanf with a format specifier of "%d %d"? Check the return value of sscanf and the results for validation.

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