Won't open files.

From man fgets: "The newline, if any, is retained". So, you are looking for a file path like:

/Users/douglasbrenner/ANDY/ct/country_data/ECHW.TXT\n

and not finding it because you don't have any files named that (note the trailing newline). What you actually have is

/Users/douglasbrenner/ANDY/ct/country_data/ECHW.TXT

with no trailing newline.



As for "produces an errno of 0.", you are printing your local variable errnum which is never initialized, so it could be anything. Sheer luck it is 0. Try using the extern int errno instead. That is what is set by these functions.

 

No problem. What I usually do when I want to print out a value and need to make sure there are no trailing spaces or newlines or other things that are hard to spot, I use printf("[%s]\n",...). In this case, that would have shown

[/path/goes/here
]

which would have been obvious. This also works if you are concerned about trailing spaces, and so on.

 

Code:

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

#define list_of_etfs "/Users/robert/Downloads/doug/etfs.txt"

#define data_dir "/Users/robert/Downloads/doug/"

extern int errno;

int main(int argc, const char * argv[]) {
  FILE *etfs, *ETF;
  char etf[15], filename[150];
  char line[200];

  //open list
  etfs = fopen(list_of_etfs, "r");
  if (etfs == NULL) {
    printf("list not open\n");
    exit(0);
  } else {
      printf("Successfully opened list of etfs");
  }
  // read etfs
  while ((fgets(etf, sizeof(etf), etfs)) != NULL)  {
    //build our new file name
    strcpy(filename, data_dir);
    strcat(filename, etf);
    strtok(filename, "\n");
    printf("\n\nRead in: %s from list of etfs\n", etf);

    ETF = fopen(filename, "r");
    if (ETF == NULL) {
      printf("%s file not opened, errno %d\n ", filename, errno);
      fprintf(stderr, "%s\n ", strerror(errno));

      exit(0);
    } else {
        printf("Successfully opened file %s\n", filename);
    }
    fclose(ETF);
  }
  fclose(etfs);
}

Fixed a bunch of other stuff for you too.

--- Post Merged, Aug 14, 2016 ---

You gotta learn Python doug

Code:

#this is a comment

#this is like an 'include' in C
import sys

list_of_etfs = "/Users/robert/Downloads/doug/etfs.txt"
data_dir = "/Users/robert/Downloads/doug/"

list_file = open(list_of_etfs)

for line in list_file:
    filename = line
    next_file = open(data_dir + filename.rstrip('\n')) # remove the \n like in C
    for l in next_file:
        sys.stdout.write(l)

Save you so much time and effort instead of trying to bash your head around handling strings and such in C