如何使用 C 语言中的 fscanf() 读取 .gro 文件？

Question

I am trying to read the following gro file via a C code.

FJP in Pol Water in water t=   0.00000 step= 0
   16
    1FJP      P    1   5.346   7.418   0.319
    2FJP      P    2   5.151   7.405   0.499
    3FJP      P    3   5.260   7.178   0.428
    4FJP      P    4   5.159   6.961   0.342
    5FJP      P    5   5.355   6.909   0.220
    6FJP      P    6   5.169   6.824   0.043
    7FJP      P    7   5.068   6.669  11.454
    8FJP      P    8   4.919   6.861  11.482
    9FJP      P    9   4.835   7.075  11.364
   10FJP      P   10   4.738   6.987  11.197
   11FJP      P   11   4.847   7.115  10.993
   12FJP      P   12   4.642   7.126  10.870
   13FJP      P   13   4.680   6.940  10.674
   14FJP      P   14   4.521   7.052  10.545
   15FJP      P   15   4.321   6.973  10.513
   16FJP      P   16   4.315   6.728  10.516
  11.56681  11.56681  11.56681

My code is:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, const char * argv[])
{
    char input_file[]="file.gro";

    FILE *input;
    char *myfile=malloc(sizeof(char)*80);

    sprintf(myfile,"%s",input_file); //the .gro file being read in
    input=fopen(myfile,"r");

double dummy1,dummy6,dummy7,dummy8,dummy9,dummy10,dummy11;
int dummy2,dummy3,dummy4,dummy5;

int lines=0;

  while (fscanf(input,"FJP in Pol Water in water t=   %lf step= %d",&dummy1,&dummy2)==2
    ||fscanf(input,"   %d\n",&dummy3)==1
    ||fscanf(input,"    %dFJP      P    %d   %lf   %lf   %lf\n",
        &dummy4,&dummy5,&dummy6,&dummy7,&dummy8)==5
    ||fscanf(input,"  %lf  %lf  %lf\n",&dummy9,&dummy10,&dummy11)==3)
  {
    printf("%lf %d\n",dummy1,dummy2);
    printf("%d\n",dummy3);
    printf("%d %d\n",dummy4,dummy5);
    printf("%lf %lf %lf\n",dummy6,dummy7,dummy8);
    printf("%lf %lf %lf\n",dummy9,dummy10,dummy11);

    lines=lines+1;
  }

  printf("lines=%d\n",lines);

    fclose(input);
}

The problem is the values printed by the various dummy variables do not match what is in the file. Also, the number of lines being read is 3 as opposed to 19, which matches the file. I am not certain what is incorrect about my fscanf() statements to read this file. Any help for this problem would be much appreciated.

Answer 1

Your main problem is that you are assuming scanf is better than it is.

Scanf will read and parse as many arguments as it can, and then give up. It does not rewind to the start of the scanf. Also it treats spaces and newlines (and tabs) as simply "skip all whitespace"

So the line printf("%d\\n",dummy3) will try to parse the main lines, eg 1FJP

It will read the digit 1 OK into dummy3, but then get stuck because P != a whitespace.

All the other rules will then get stuck, because none of them expect a P or any string first.

If you want to do it this way, you will just have to apply the scanf statements more intelligently as and when they are expected.

Answer 2

The problem is that you try to read and match the header repeatedly, before each line read (in the while loop.) you should read the head once, then read the lines. You also only need to skip any given piece of whitespace once. So you end up with code like:

if (fscanf(input,"FJP in Pol Water in water t=%lf step=%d%d", &dummy1, &dummy2, &dummy3) != 3) {
    fprintf(stderr, "Invalid header\n");
    exit(1); }
while (fscanf(input,"%dFJP P%d%lf%lf%lf", &dummy4, &dummy5, &dummy6, &dummy7, &dummy8) == 5)  {
    ... read a line of the table