Reading a file character by character in C

Question

I m writing a BF interpreter in C and I ve run into a problem reading files  I used to use scanf in order to read the first string  but then you couldn t have spaces or comments in your BF code   Right now here is what I have   char  readFile char  fileName      FILE  file    char  code   malloc 1000   sizeof char      file   fopen fileName   r      do           code      char fgetc file        while  code    EOF     return code      I know the problem arises in how I m assigning the next char in the file to the code pointer but I m just not sure what that is  My pointer knowledge is lacking  which is the point of this exercise  The interpreter works fine  all using pointers  I m just having a problem reading files in to it    I m going to implement only reading  - gt  lt      into the file later  although if anyone has a good way to do it  it would be great if you d let me know

User · Answer

Either of the two should do the trick -

char *readFile(char *fileName)
{
  FILE *file;
  char *code = malloc(1000 * sizeof(char));
  char *p = code;
  file = fopen(fileName, "r");
  do 
  {
    *p++ = (char)fgetc(file);
  } while(*p != EOF);
  *p = '\0';
  return code;
}

char *readFile(char *fileName)
{
  FILE *file;
  int i = 0;
  char *code = malloc(1000 * sizeof(char));
  file = fopen(fileName, "r");
  do 
  {
    code[i++] = (char)fgetc(file);
  } while(code[i-1] != EOF);
  code[i] = '\0'
  return code;
}

Like the other posters have pointed out, you need to ensure that the file size does not exceed 1000 characters. Also, remember to free the memory when you're done using it.

User · Answer

There are a number of things wrong with your code   char  readFile char  fileName        FILE  file      char  code   malloc 1000   sizeof char        file   fopen fileName   r        do               code      char fgetc file          while  code    EOF       return code       What if the file is greater than 1 000 bytes  You are increasing code each time you read a character  and you return code back to the caller  even though it is no longer pointing at the first byte of the memory block as it was returned by malloc   You are casting the result of fgetc file  to char  You need to check for EOF before casting the result to char    It is important to maintain the original pointer returned by malloc so that you can free it later  If we disregard the file size  we can achieve this still with the following   char  readFile char  fileName        FILE  file   fopen fileName   r        char  code      size t n   0      int c       if  file    NULL          return NULL    could not open file      code   malloc 1000        while   c   fgetc file      EOF                code n       char  c                don t forget to terminate with the null character     code n      0                return code      There are various system calls that will give you the size of a file  a common one is stat

User · Answer

I think the most significant problem is that you re incrementing code as you read stuff in  and then returning the final value of code  i e  you ll be returning a pointer to the end of the string   You probably want to make a copy of code before the loop  and return that instead   Also  C strings need to be null-terminated   You need to make sure that you place a   0  directly after the final character that you read in   Note  You could just use fgets   to get the entire line in one hit

User · Answer

the file is being opened and not closed for each call to the function also

User · Answer

Here s one simple way to ignore everything but valid brainfuck characters    define BF VALID   - gt  lt        if  strchr BF VALID  c       code n      c

User · Answer

The problem here is twofold    a  you increment the pointer before you check the value read in  and  b  you ignore the fact that fgetc   returns an int instead of a char    The first is easily fixed   char  orig   code     the beginning of the array        do      code   fgetc file     while  code      EOF    code     0      nul-terminate the string return orig     don t return a pointer to the end   The second problem is more subtle -fgetc returns an int so that the EOF value can be distinguished from any possible char value  Fixing this uses a temporary int for the EOF check and probably a regular while loop instead of do   while

User · Answer

Expanding upon the above code from  dreamlax  char  readFile char  fileName        FILE  file   fopen fileName   r        char  code      size t n   0      int c       if  file    NULL  return NULL    could not open file     fseek file  0  SEEK END       long f size   ftell file       fseek file  0  SEEK SET       code   malloc f size        while   c   fgetc file      EOF            code n       char c             code n      0                return code      This gives you the length of the file  then proceeds to read it character by character

[c] Reading a file character by character in C

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