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How do dev files work?

How the guys from Linux make files /dev. You can write to them, and they are immediately erased. I can imagine some program that constantly reads the dev file:

FILE *fp;
char buffer[255];
int result;
fp = fopen(fileName, "r");
if (!fp) {
    printf("Open file error");
    return;
}
while (1)
{

    result = fscanf(fp, "%254c", buffer);
    printf("%s", buffer);
    memset(buffer, 0, 255);
    fflush(stdout);
    sleep(1);
}
fclose(fp);

But how to remove content? Closing the file and opening them again in "w" mode is not the way they did, because you can do iecat > /dev/tty

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