Question

I want to read 80 characters from a text file, save them to a string and then print that string for verification.
I am using fread and have this code:

char message[80];
size_t nread = fread(message, 1, sizeof(message), fp);
printf("Message received: \"__%s__\"\n", message);

And the output is:

Message received: “__I would love to change the world but they won’t
��__”

when the whole phrase isn’t in the file

and:

__I would love to change the world but they won’t give me the source code
@__

when the whole phrase is in the file.

I’ve tried deleting it and rewriting the text but I get the same output again.

What is wrong? Something with the charset?

Answer 1

fread() does not null terminate the buffer and prinf("%s") expects the buffer to be null terminated. As the buffer is not null terminated printf() will continue reading until it finds a null terminator, printing out any junk along the way.

Either null terminate the buffer, remembering to leave room for the null terminator:

char message[81]; /* Increased by 1 for null terminator. */
size_t nread = fread(message, 1, sizeof(message) - 1, fp);
message[nread] = 0;
printf("Message received: \"__%s__\"\n", message);

or instruct printf() to only print the number of characters read using "%.*s" format specifier:

printf("Message received: \"__%.*s__\"\n", nread, message);