Silly C hacks

Macros! To do safe mallocs and fopens! Brittle like the glass you tread upon!

/* A small cat that prints out the files given to it */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <malloc.h>
#include <sys/stat.h>

#define BLOCK(pre, post, ok, error, block) \
  { \
    pre; \
    if (ok) { \
      block; \
      post; \
    } else { \
      error; \
    } \
  }

#define with_malloc(t, var, sz, block) \
  BLOCK(t var = (t)malloc(sz), free(var), var, \
        fprintf(stderr, "Malloc failed, out of memory\n"); exit(1), block)

#define with_file(var, fn, mode, error, block) \
  BLOCK(FILE* var = fopen(fn, mode), fclose(var), var, error, block)

#define with_file_contents(var, len, fn, error, block) \
  with_file(var##__f, fn, "r", error, \
    off_t len = file_size(fn); \
    with_malloc(char*, var, len+1, \
      len = fread(var, 1, len, var##__f); \
      var[len] = 0; \
      block))

off_t file_size(char *path)
{
  struct stat st;
  stat(path, &st);
  return st.st_size;
}

int main(int argc, char *argv[]) {
  int i;
  for (i=1; i<argc; i++) {
    with_file_contents(s, slen, argv[i], fprintf(stderr, "Couldn't open %s.\n", argv[i]),
      fwrite(s, 1, slen, stdout);
    );
  }
}

It would be kinda fun to port the whole functional array-munging part of prelude.ml to C. Fun in a very painful fashion.