Question

I am working on a log parsing program that retrieves the file to open by combining an environment variable and a preset string in order to provide the full path to the file, but i am having trouble getting fopen to take out the output from sprintf which i am using to combine the environment variable and the preset string,so i was wondering if anyone could offer advice on what i should do to get this to work properly? thanks! (i have just begun teaching myself C over the last few weeks, so im open to any tips no matter how obvious they should be to me)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define _GNU_SOURCE
void main(int argc, char *argv[], char *envp[])
{
  FILE *fd; // File pointer
  char *name;
  char *filename[];
  name = getenv("MCEXEC_PLAYERNAME");
  sprintf(filename,"/home/minecraft/freedonia/playerdata/deathlog-%s.txt",name);
  char buff[1024];
  if ((fd = fopen(filename, "r")) != NULL) // open file
  {
    fseek(fd, 0, SEEK_SET); // make sure start from 0

    while(!feof(fd))
    {
      memset(buff, 0x00, 1024); // clean buffer
      fscanf(fd, "%[^\n]\n", buff); // read file *prefer using fscanf
    }
    printf("Last Line :: %s\n", buff);
  }
  else
  printf( "fail" );
}

here is the error i get while compiling using gcc

lastline.c: In function ‘main’:
lastline.c:9: error: array size missing in ‘filename’
lastline.c:11: warning: passing argument 1 of ‘sprintf’ from incompatible pointer type
/usr/include/stdio.h:341: note: expected ‘char * __restrict__’ but argument is of type   ‘char **’
lastline.c:13: warning: passing argument 1 of ‘fopen’ from incompatible pointer type
/usr/include/stdio.h:249: note: expected ‘const char * __restrict__’ but argument is of   type ‘char **’

Answer 1

char *filename[];

declares an array of pointers to char of unknown size. You need an array of char to sprintf to, of sufficient known length. Declare

char filename[1000];  // assuming 1000 is large enough

or

char *filename;

as a pointer to char and malloc sufficient memory after you have gotten the name,

filename = malloc(sizeof "/home/minecraft/freedonia/playerdata/deathlog-.txt" - 1 + strlen(name) + 1);
if (!filename) exit(EXIT_FAILURE);

to avoid unpleasant surprises if name turns out longer than expected.