Vitis - implicit declaration of 'read'; did you mean 'fread'

[Hartley]

Hello all,

I have a build warning in my code:

implicit declaration of 'read'; did you mean 'fread'? [-Wimplicit-function-declaration]

The code works but the warning is annoying.

I tried including <unistd.h> to pull in the declaration but that results in a build failure:

conflicting types for 'sleep'
conflicting types for 'usleep'

Does anyone know what header can be included in Vitis to correctly get the prototype of 'read'?

Thanks

[artvvb]

Hi @Hartley

Assuming your project is a baseline Baremetal project, file I/O isn't necessarily implemented. You might need to bring in additional libraries that allow you to interact with a file system on, for example, an SD card. - I assume it's not baremetal if read works despite the warning.

What's your project? Is this Vitis HLS or "plain-old" Vitis? Is this a petalinux project?

Thanks,

Arthur

[Hartley]

My project is a baseline Baremetal project.

I'm using read() to get input from STDIN to allow user input of simple commands to test my hardware design. Basically:

static void read_input(char* str) {
    printf("> ");
	fflush(stdout);
	int index = 0;
	char key;
	do {
		read(1, (char*)&key, 1);
		switch (key) {
		case 0x0D:	// enter
			printf("\r\n");
			break;
		case 0x7F:	// backspace
			if (index > 0) {
				index--;
				str[index] = 0x00;
				printf("\r                                                  \r");
				fflush(stdout);
				xil_printf("> %s", str);
				fflush(stdout);
			}
			break;
		default:
			str[index++] = key;
			printf("%c", key);
			fflush(stdout);
		}
	} while (key != 0x0D);
	str[index] = 0x00;
}

The function works fine I just wanted to get rid of the annoying warning during the build.

read() is normally defined in <unistd.h> but including that breaks the build due to the conflicting types for 'sleep' and 'usleep'.

But, read() must be available somehow since the code does run. I was just wondering where so I can include the proper header.