CODEWITHSUNDEEP
cfileparsingstrtok
nhenrique
nhenrique

Reputation: 894

Parse file in C to read char

Let's say i have a file filled with random characters with whitespaces and \n included also random.

I want to look for this groups of chars, example: UU, II, NJ, KU. So the purpose is to read the file, look for this kind of groups and say how many are they in the file.

My problem is whitespace and \n, becase if i find one of these i should skip it and search again for the groups. I found a solution that could help me, the function strtok_r .

http://www.codecogs.com/reference/computing/c/string.h/strtok.php?alias=strtok_r

i think this will isolate full strings so i can read one at time.

Is it a good solution or should take other approach?

Upvotes: 0

Views: 1199

Answers (2)

Leblanc Meneses
Leblanc Meneses

Reputation: 3091

You could also use

https://github.com/leblancmeneses/NPEG/tree/master/Languages/npeg_c

if your search pattern becomes more difficult.

Here is a visual tool that can export C version: http://www.robusthaven.com/blog/parsing-expression-grammar/npeg-language-workbench

Documentation for rule grammar: http://www.robusthaven.com/blog/parsing-expression-grammar/npeg-dsl-documentation

Rules

    (?<UU>): 'UU'\i; 
(?<II>): 'II'\i; 
(?<NJ>): 'NJ'\i; 
(?<KU>): 'KU'; // does not use \i so is case sensitive 

Find: UU / II / NJ / KU;
(?<RootExpression>): (Find / .)+;

Input 1:

 UU, II, NJ, KU  uu, ii, nJ, kU

Input 2:

jsdlfj023#uu, ii, nJ, kU $^%900oi)()*()  UU, II, NJ, KU

Upvotes: 0

Some programmer dude
Some programmer dude

Reputation: 409482

A naive solution would probably to read one character at a time, and when it's 'U', 'I', 'N' or 'K' then read another character to see if it's the next character in the group. If it is then increase a counter for that group. All other characters are simply discarded.

Edit: Example function:

int count_uu = 0;
int count_ii = 0;
int count_nj = 0;
int count_ku = 0;

void check_next_char(int expected, FILE *input, int *counter);

void count(FILE *input)
{
    int ch;  /* Character we read into */

    while ((ch = fgetc(input)) != EOF)
    {
        switch (ch)
        {
        case 'U':
            check_next_char('U', input, &count_uu);
            break;
        case 'I':
            check_next_char('I', input, &count_ii);
            break;
        case 'N':
            check_next_char('J', input, &count_nj);
            break;
        case 'K':
            check_next_char('U', input, &count_ku);
            break;

        default:
            /* Not a character we're interested in */
            break;
    }
}

/* This function gets the next character from a file and checks against
   an `expected` character. If it is same as the expected character then
   increase a counter, else put the character back into the stream buffer */
void check_next_char(int expected, FILE *input, int *counter)
{
    int ch = fgetc(input);
    if (ch == expected)
        (*counter)++;
    else
        ungetc(ch, input);
}

Upvotes: 4

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