Temporary files in C

tmpfile gives you a stream that deletes itself when it is closed.

#include <stdio.h>

int roundtrip(void) {
    FILE *f = tmpfile();
    if (f == NULL) {
        return 0;
    }
    fprintf(f, "42 rust\n");
    rewind(f);

    int number = 0;
    char word[16];
    int matched = fscanf(f, "%d %15s", &number, word);
    fclose(f);
    return matched == 2 && number == 42;
}

How it works

1. There is no name to clean up afterwards.
2. It opens in binary update mode, so you can write then read.
3. rewind before reading back what you just wrote.

Keywords and builtins used here

• FILE
• NULL
• char
• if
• int
• return
• roundtrip
• void

The run, in numbers

Lines

16

Characters to type

260

Tokens

90

Three-star pace

100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 54 seconds.

Type this snippet

Step 4 of 4 in Writing & binary, step 8 of 12 in Files & I/O.

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