how to detect end of line

This is a discussion on how to detect end of line within the C Programming forums, part of the General Programming Boards category; Hi. I'm reading integers from a file and placing them into an array. How do you detect for end-of-line? I've ...

  1. #1
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    how to detect end of line

    Hi. I'm reading integers from a file and placing them into an array.
    How do you detect for end-of-line? I've tried checking using '\0' and '\n', neither works.
    If I can detect the end-of-line then I can remove the 0 that adds itself to the array.

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <ctype.h>
    #include <math.h>
    
    int main()
    {
       /*Initialisations*/
       FILE *fin;
       char file_name_in[20]= "test.txt",c;
       long int int_array[10000],temp_array[1000],d,j=0,k=0,temp_integer=0,size_of_array=0;
    
       /* Test to see if file opens */
       fin = fopen(file_name_in, "r");
       if (fin == NULL){
          (void)fprintf(stderr,"Cannot open input file %s\n",file_name_in);
       }
    
       int i=0;
       do{
          c = getc(fin);
          if (((c == ' ')||(c == '\0'))&&(i!=0)){
             temp_integer = 0;
             for (j=0;i>0;j++){
                i-=1;
                temp_integer += (pow(10,i))*temp_array[j];
             }
             int_array[k] = temp_integer;
             printf("\nint_array at position %d is %d\n",k,int_array[k]);
             k++;
          }
          d = atoi(&c);
          temp_array[i]= d;
          i++;
       }while (c!=EOF);
    
       return 0;
    }
    sample input data:
    2 300
    4 800
    10 10
    10 10
    10 10
    10 100
    10 10

    The output:
    int_array at position 0 is 2

    int_array at position 1 is 30004

    int_array at position 2 is 800010

    int_array at position 3 is 10010

    int_array at position 4 is 10010

    int_array at position 5 is 10010

    int_array at position 6 is 100010

    Any Ideas?

  2. #2
    Programming King Mr.777's Avatar
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    You can check a string whether it contains an end-of-line sequence by testing for the character '\n', of course, but there isn't a function to tell you that the current file position is "at the end of a line".
    If you have a line-based file format, it's sometimes easiest to use two levels of parsing. First, read in a whole line using the global std::getline function. Then use an std::istringstream to parse that as necessary. Repeat for each line in the input file.
    You should generally never need to ever use eof() directly, of course. Just keep reading lines until the stream evaluates to false in a boolean context.
    Forexample:
    Code:
    std::ifstream input("input.dat");
    std::string line;
    // For each line...
    while (std::getline(input, line)) {    
                                           std::istringstream iss(line);
                                           char c;
        // For each character token...    
                                                     while (iss >> c) {      
      // Do something with c                                      }
                                                      }

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    Or use fgets() since this is the C forum.
    If you understand what you're doing, you're not learning anything.

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    Quote Originally Posted by a_satari View Post
    Hi. I'm reading integers from a file and placing them into an array.
    Are they integers or are they ascii characters? From your code I get that you are reading a string from a file. I don't get what you are doing in the if clause in the do/while loop, it seems like you would want to advance the file pointer there. But you are probably better of using fgets().

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    Programming King Mr.777's Avatar
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    I don't think if fgets() will work as it just reads the whole file till the end of file marker or just allows to input a single string till the '/n'....

    I didn't check but logically it seems to be like this.....

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    Well, you can wrap the fgets call inside a while loop condition, then do the conversion inside the loop body. fgets() does what getline does.

  7. #7
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    Quote Originally Posted by Mr.777 View Post
    Forexample:
    Code:
    std::ifstream input("input.dat");
    std::string line;
    Not in C you won't.... That's C++ code.

  8. #8
    Programming King Mr.777's Avatar
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    Quote Originally Posted by CommonTater View Post
    Not in C you won't.... That's C++ code.
    Yup... Sorry... My bad ;-)

  9. #9
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    what I'm really trying to ask is, how do you determine end of line?
    In my outputs, the end of line is represented as a 0.
    I want to get rid of this. So far I've used if statements to check for the following :
    '/n'
    '/0'
    NULL
    0x20 - which I think is ascii for end of line.

    none of which have worked.

  10. #10
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    Quote Originally Posted by a_satari View Post
    what I'm really trying to ask is, how do you determine end of line?
    In my outputs, the end of line is represented as a 0.
    I want to get rid of this. So far I've used if statements to check for the following :
    '/n'
    '/0'
    NULL
    0x20 - which I think is ascii for end of line.

    none of which have worked.
    I don't really understand how 0 marks the end of your lines. So what happens when you read in "10 100". One of those 0s marks the end of your line?

    Anyway, some problems with what you've tried:

    1) '/n', this is a multi-character constant and is invalid. You're looking for '\n', which is the traditional end-of-line marker
    2) Again, '/0' is a multi-character constant and is invalid. You're looking for '\0', which marks the end of a string, but not a line in a text file.
    3) NULL, this is used to indicate an invalid pointer.
    4) 0x20, is the ASCII symbol for a space.
    If you understand what you're doing, you're not learning anything.

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    Thanks itsme86. I don't completely understand how 0 marks the end of line either.
    I think it may be to do with reading the character using getc then converting it to an int using
    atoi.
    I'm going to try a few thing using getw which I'm told reads integers.

  12. #12
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    I think itsme86 was suggesting that 0 doesn't actually mark the end of your lines. The end of a line is marked with '\n'. The end of a string is marked with '\0'. As for getc, it already returns an int (not a char, see: Question 12.1). Trying to use atoi on the result will likely give you a seg fault, since atoi expects a char pointer. getw is most likely not what you want. It is for reading a binary word, not a text word.

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