[SOLVED] A problem. When using assembly language to call the C language function

mirage1993 · 10-03-2014, 05:49 AM

I use assembly language to call the C language function.And I have a problem.

main.s

Code:

.section .data
a:
	.int 10
b:
	.int 20
.section .text
.globl main
.type main,@function
main:
	movl $a,%eax
	movl $b,%ebx
	pushl %ebx
	pushl %eax
	call _swapint
	movl $1,%eax
	movl $0,%ebx
	int $0x80

pro.c

Code:

#include<stdio.h>
int _swapint(int *a,int *b)
{
int c;
printf("!!!");
c=*a;
*a=*b;
*b=c;
printf("success!");
return 0;
}

I am sure that the value of a and b have been swapped,but I can't see any output! I can't understand.

thx.

mirage1993 · 10-03-2014, 07:24 AM

when I use

Code:

puts("success");

It's OK!
but,why??

Guttorm · 10-03-2014, 07:42 AM

It's because puts adds a newline, and stdout is line buffered, so you don't see anything until you output a newline.

mirage1993 · 10-03-2014, 08:15 AM

Quote:

Originally Posted by Guttorm

It's because puts adds a newline, and stdout is line buffered, so you don't see anything until you output a newline.

thank you very much！！