C Interview Questions and Answers

 

How can I read data from data files with particular formats?

How can I read data from data files with particular formats?



How can I read ten floats without having to use a jawbreaker scanf format



like "%f %f %f %f %f %f %f %f %f %f"?



How can I read an arbitrary number of fields from a line into an array?





In general, there are three main ways of parsing data lines:


1. Use fscanf or sscanf, with an appropriate format string. Despite the limitations
mentioned in this section, the scanf family is quite powerful. Though whitespace-separated
fields are always the easiest to deal with, scanf format strings can also be used
with more compact, column oriented, FORTRAN-style data. For instance, the line



1234ABC5.678



could be read with "%d%3s%f".



, then deal with each field individually, perhaps with functions like atoi and atof.
(Once the line is broken up, the code for handling the fields is much like the traditional
code in main() for handling the argv array;



Break the line into fields separated by whitespace (or some other delimiter), using
strtok or the equivalent This method is particularly useful for reading an arbitrary
(i.e. not known in advance) number of fields from a line into an array.



Here is a simple example which copies a line of up to 10 floating-point numbers
(separated by whitespace) into an array:



#define MAXARGS 10



char line[] = "1 2.3 4.5e6 789e10";



char *av[MAXARGS];



int ac, i;



double array[MAXARGS];





ac = makeargv(line, av, MAXARGS);



for(i = 0; i < ac; i++)



array[i] = atof(av[i]);

Posted by:Richards