在C linux中打开文件

Question

I am using C to open a file for reading. I have this code :

fp = fopen("./settings.cfg","r");
if (fp != NULL)
    printf("OK");
else
    printf("ERROR");

but I always get an error.

The file is located in the folder where the executable resides. I have tried writing only "settings.cfg". What might be the problem?

Answer 1

Try perror() to have the library itself tell you what, if anything, is wrong.

fp = fopen("./settings.cfg", "r");
if (fp != NULL)
    printf("OK\n");
else perror("fopen");

Answer 2

You are opening the file in the "current directory", not "in the folder where the executable is".

In fact, unix has no easy way to find that particular folder; in Linux you could readlink() the /proc/[your pid]/exe link to find the executable and strip off the filename portion -- that will work in many cases, but there are some fringe cases like hardlinks that will make it fail.

Answer 3

From which directory do you run the program? It won't have the directory where it resides as the current directory, it will be inherited from the environment.

Could also be rights, that the file is owned by someone else and you don't have read rights.

Also double-check the filename. This sounds obvious, but do it anyway.

Answer 4

If file you are trying to open is in the same directory of your C compiled file, you must simply do

fp = fopen("settings.cfg","r");
if (fp != NULL)
  printf("OK");
else
  printf("ERROR");

without the initial " ./ " at the file's name