Correct way to read a text file into a buffer in C

Question

This question already has an answer here:

• How to read the content of a file to a string in C? 9 answers

I'm dealing with small text files that i want to read into a buffer while i process them, so i've come up with the following code:

...
char source[1000000];

FILE *fp = fopen("TheFile.txt", "r");
if(fp != NULL)
{
    while((symbol = getc(fp)) != EOF)
    {
        strcat(source, &symbol);
    }
    fclose(fp);
}
...

Is this the correct way of putting the contents of the file into the buffer or am i abusing strcat()?

I then iterate through the buffer thus:

for(int x = 0; (c = source[x]) != '\0'; x++)
{
    //Process chars
}

Answer 1

Not tested, but should work.. And yes, it could be better implemented with fread, I'll leave that as an exercise to the reader.

#define DEFAULT_SIZE 100
#define STEP_SIZE 100

char *buffer[DEFAULT_SIZE];
size_t buffer_sz=DEFAULT_SIZE;
size_t i=0;
while(!feof(fp)){
  buffer[i]=fgetc(fp);
  i++;
  if(i>=buffer_sz){
    buffer_sz+=STEP_SIZE;
    void *tmp=buffer;
    buffer=realloc(buffer,buffer_sz);
    if(buffer==null){ free(tmp); exit(1);} //ensure we don't have a memory leak
  }
}
buffer[i]=0;

Answer 2

Have you considered mmap()? You can read from the file directly as if it were already in memory.

http://beej.us/guide/bgipc/output/html/multipage/mmap.html