help reading from file

English Programming/Scripting
#1

Hello

I am supposed to read IPs from a file. In the following code I have replaced the processing part with simple printfs. The point is the number of IPs is not known but they are arranged in ranges each
on a new line, e.g.
2.3.4.5-10.255.255.255

With the following code, I could get all digits correct except the first digit. Please suggest.

while((a=getc(stdin))!=EOF){
ungetc(a, stdin);
for(i=0;i<4;i++){
fscanf(stdin, “%d”, &a);
printf("%d
“, a);
fscanf(stdin, " %c”, &c);
}
for(i=0;i<4;i++){
fscanf(stdin, “%d”, &a);
printf("%d
“, a);
fscanf(stdin, " %c”, &c);
}
}

Thank you.

#2

Why not just read in the whole line and parse it with one sscanf?


char line[256];
int a1, a2, a3, a4, b1, b2, b3, b4;
while (fgets(line, sizeof(line), stdin) != NULL) {
    int status = sscanf(line, "%d.%d.%d.%d-%d.%d.%d.%d", &a1, &a2, &a3, &a4, &b1, &b2, &b3, &b4);
    if (status < 8)
        // not enough values
    else
        // process data
}
#3

is this homework such that you are restricted to using C? if not, use dedicated parsing tools, eg awk (or better languages suited for parsing files, eg Python,Perl) will be better.

#4

ghostdog74 wrote:
> is this homework such that you are restricted to using C? if not, use
> dedicated parsing tools, eg awk (or better languages suited for parsing
> files, eg Python,Perl) will be better.
>
>
This is not homework but personal indulgence. Thank you for the suggestion; I will have a look at those tools for sure.

Thank you.

#5

ken yap wrote:
> Why not just read in the whole line and parse it with one sscanf?
>
> Code:
> --------------------
>
> char line[256];
> int a1, a2, a3, a4, b1, b2, b3, b4;
> while (fgets(line, sizeof(line), stdin) != NULL) {
> int status = sscanf(line, “%d.%d.%d.%d-%d.%d.%d.%d”, &a1, &a2, &a3, &a4, &b1, &b2, &b3, &b4);
> if (status < 8)
> // not enough values
> else
> // process data
> }
> --------------------
>
>
Initially, I was also thinking of getting strings from files extracting the integers; but my method of parsing was inefficient. Thank you ken.

#6

Cross_AM wrote:
> Hello
>
> I am supposed to read IPs from a file. In the following code I have replaced the processing part with simple printfs. The point is the number of IPs is not known but they are arranged in ranges each
> on a new line, e.g.
> 2.3.4.5-10.255.255.255
>
> With the following code, I could get all digits correct except the first digit. Please suggest.
>
> while((a=getc(stdin))!=EOF){
> ungetc(a, stdin);
> for(i=0;i<4;i++){
> fscanf(stdin, “%d”, &a);
> printf("%d
“, a);
> fscanf(stdin, " %c”, &c);
> }
> for(i=0;i<4;i++){
> fscanf(stdin, “%d”, &a);
> printf("%d
“, a);
> fscanf(stdin, " %c”, &c);
> }
> }
>
> Thank you.
Friends, we all know that there are numerous workarounds to this problem; but what I wanted was to understand is what is causing the problem.

#7

Sorry mate, I gave up on trying to understand learners’ code way back when I was a uni tutor. :frowning: I don’t want to go back to those days. These days I just write code my way. You’ll have to nut this one out without my help.

#8

ken yap wrote:
> Sorry mate, I gave up on trying to understand learners’ code way back
> when I was a uni tutor. :frowning: I don’t want to go back to those days. These
> days I just write code my way. You’ll have to nut this one out without
> my help.
>
>
Thanks neways ken.