Question

I need to create a search program in C language, that can parse the text file and find the keyword x=”value”. then I want to create a list of value items into array. Currently I am using fscanf approach, here is my code snippet.

    fscanf(fp, "%s", buf);
    if !strcmp(buf, "x")
    {
       fscanf(fp, "%s", buf);
        if ( ! strcmp(buf, "="))
         fscanf(fp, "%s", buf);
        else
        printf("\n Not a valid format");
    }

I don’t want to use fscanf, Is there any other approach for my requirement??

Thanks.

Answer 1

There are other approaches (e.g., you could use Flex), but I think slightly better use of sscanf would make the most sense:

char buffer[256];
char value[128];

fgets(buffer, sizeof(buffer), fp);

if (1==sscanf(buffer, "x=%127s", value))
     // we read a value -- now use it however needed.

Edit: The basic idea here is pretty simple. We start by reading a whole like with fgets. We then use sscanf to try to match x=<whatever> in that line. If we find it, we have the value we care about. If we didn’t find it, sscanf will return 0, since it returns the number of items it converted — and if it doesn’t match the x= we specified, it won’t convert anything, so sscanf will return 0, and we know that line didn’t match.

Edit 2: Here’s a small demo program that reads data from a file, and prints out the values for lines that follow the form x=<whatever>, with spaces allowed before and after the x and the =:

#include <stdio.h>

int main() { 

    FILE *infile = fopen("Somefile.txt", "r");

    char buffer[256];
    char value[128];

    while (fgets(buffer, sizeof(buffer), infile))
        if (1 == sscanf(buffer, " x = %127s", value))
            printf("Value = %s\n", value);
    return 0;
}

I tested it with this as input:

some junk
#a comment
a = 1 ; a couple other variables.
b = 2
x = 3
 x = 4
x=5

The result I got was:

Value = 3
Value = 4
Value = 5