fscanf only reading only one integer but assigning to multiple variables

Question

Ive been working on a project all day and I have come to a hault because fscanf isn't working the way I thought it was suppose to.

I am reading a file that contains something like this:

AND 0 3 2

Here is a peice of my code that is giving me problems:

while(fscanf(circuit, "s",cur_gate)!=EOF){
    if(cur_gate[0]=='A'){
            fscanf(circuit,"%d %d %d",&cur_output,&cur_input1,&cur_input2);
            printf("current output: %d\n",cur_output);
            printf("current input: %d current input2: %d\n",cur_input1,cur_input2);

So what I am doing is reading the file and checking if the string = AND (cur_gate). Then if it = 'A', i am reading 3 integers. I want to assign the first integer to cur_output and the second and third to cur_input1 and cur_input2, respectively.

The problem is that its output is:

current output: 0

current input: 0 current input2: 0

While the output should actually be:

current output: 0

current input: 3 current input2: 2

I honestly don't know what's wrong because I did almost the same thing earlier and it worked. Thanks for any help!

score 1 · Accepted Answer · edited May 23 '17 at 12:33

1

fscanf(circuit, "s",cur_gate) will try to scan a literal s character. If you want to scan a string, you'll need something like %s.

This would have been more obvious if you had followed the "check for what you want rather than don't want" rule of scanf:

while (fscanf (circuit, "s",cur_gate) == 1) {

What's happening in your case is that the scan for the literal s is failing but not in such a way that it returns EOF. So, when you come to scanning in the integers (the buffer must have an A as the first character to get inside the if loop), they fail as well because the input stream pointer is still on the A at the start of AND.

As an aside, unless you control the input, using fscanf here can lead to buffer overflow problems. There are probably better ways to do it.

edited May 23 '17 at 12:33

Community

1
1

answered Nov 04 '15 at 04:35

paxdiablo

854,327
234
1,573
1,953

Thank you! I can't believe I didn't catch that. I was so focused on the inside of the while loop that I overlooked that. If you can't tell I am very much a rookie. Thanks – DarkLink Nov 04 '15 at 04:39
@Ryan, we *all* were once though, for us old farts, it's sometimes hard to recall :-) – paxdiablo Nov 04 '15 at 04:40

score 0 · Answer 2 · answered Nov 04 '15 at 04:36

Try this :

while(fscanf(circuit, "%s",cur_gate)!=EOF){
    if(cur_gate[0]=='A'){
            fscanf(circuit,"%d %d %d",&cur_output,&cur_input1,&cur_input2);
            printf("current output: %d\n",cur_output);
            printf("current input: %d current input2: %d\n",cur_input1,cur_input2);

Changes :

"s" -> "%s"

fscanf only reading only one integer but assigning to multiple variables

2 Answers2