One exit, everything freed in C

The acquire-check-goto pattern, written out in full.

#include <stdio.h>
#include <stdlib.h>

int process(const char *path, size_t n) {
    int result = 0;
    int *buffer = NULL;
    char *scratch = NULL;

    FILE *f = fopen(path, "rb");
    if (f == NULL) {
        goto done;
    }
    buffer = malloc(n * sizeof(int));
    if (buffer == NULL) {
        goto close_file;
    }
    scratch = malloc(n);
    if (scratch == NULL) {
        goto free_buffer;
    }

    result = (int) fread(scratch, 1, n, f);

    free(scratch);
free_buffer:
    free(buffer);
close_file:
    fclose(f);
done:
    return result;
}

How it works

1. Each acquisition has a label to unwind to.
2. Labels appear in reverse order of acquisition.
3. Nothing is freed twice and nothing is missed.

Keywords and builtins used here

• FILE
• NULL
• char
• const
• goto
• if
• int
• process
• return
• size_t
• sizeof

The run, in numbers

Lines

31

Characters to type

468

Tokens

144

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 82 seconds.

Type this snippet

Step 2 of 2 in Errors & cleanup, step 9 of 11 in APIs, errors & testing.

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