Thread: How to assign an ASCII character via inline assembly code

I am having difficulties executing a short __asm__() exercise:
Write assembly code to store char 'A' into bufone[0].

I would think it should look like this:

Code:

#include <stdio.h>

char* bufone;

int main(int argc, char* argv[])
{
	__asm__("movl $0x41, bufone\n");
	printf("\n%s\n", bufone[0]);
	return 0;
}

However, I keep getting Segmentation Fault errors. What am I missing?

Originally Posted by LanguidLegend

I am having difficulties executing a short __asm__() exercise:
Write assembly code to store char 'A' into bufone[0].

I would think it should look like this:

Code:

#include <stdio.h>

char* bufone;

int main(int argc, char* argv[])
{
	__asm__("movl $0x41, bufone\n");
	printf("\n%s\n", bufone[0]);
	return 0;
}

However, I keep getting Segmentation Fault errors. What am I missing?

Have you allocated storage for bufone?

Code:

#include <stdio.h>

char bufone[2] = {};

int main(int argc, char* argv[])
{
		__asm__("\
				movl $'A', bufone\n\
	");
	
	printf("\n%s\n", bufone[0]);
	return 0;
}

gives me this message:
buffOF1.c: In function ‘main’:
buffOF1.c:11: warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘int’
But if I change

Code:

printf("\n%s\n", bufone[0]);

to

Code:

printf("\n%x\n", bufone[0]);

I get 41.

I think you want "%c" to print out the ASCII character.

Code:

printf("\n%s\n", bufone[0]);

The %s means this would try to print a string (which is really a null-terminated array of characters). bufone[0] is not (cannot be) a string. It's a single element of an array.

Code:

printf("\n%x\n", bufone[0]);

The %x means it prints the value, in hex, of bufone[0]. bufone[0] holds the character 'A' which is 0x41 or 65d in ASCII.