A question about atomic operation in C, help!

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C

Processor: Intel Xeon E3-1230 v2
OS: Win 7 64bit
Compiler: GCC

The code is shown below:

// sample.c
#include <stdio.h>

int atomic_add_int(volatile int * address, int value){
	
	asm volatile ("lock xadd %0, %1" : <-- line 11
		"+r" (value) :
		"+m" (*address) :
		"memory");   // <-- line 14
	
	return value;
}

int atomic_inc_int(int * address){
	
	asm volatile("lock inc %0": : <-- line 21
		"+m" (*address):
		"memory");  // <-- line 23
	
	return (*address);
}

int main(){
	
	
}

When I compile the code(>gcc -c sample.c), the errors occur:
sample.c: In function 'atomic_add_int':
sample.c:14:3: error: input operand constraint contains '+'
sample.c: In function 'atomic_inc_int':
sample.c:23:3: error: input operand constraint contains '+'
sample.c:21:2: error: input operand constraint contains '+'
sample.c: In function 'atomic_add_int':
sample.c:11:2: error: input operand constraint contains '+'

I wrote the code as the book(Multicore Application Programming) tell me to, but why those error occur? Can any one help me? Thanks.