为什么省略printf打印垃圾的参数？(Why does omitting an argument to printf print garbage?)

为什么省略printf打印垃圾的参数？(Why does omitting an argument to printf print garbage?)

我通过汇编代码使用printf。 我注意到在下面的例子中，如果我省略了期望的参数，垃圾被打印。

.386 .model flat, c .stack 100h printf PROTO arg1:Ptr Byte, printlist:VARARG .data msg3fmt byte 0Ah,"%s",0Ah,"test output",0Ah,0 .code main proc INVOKE printf, ADDR msg3fmt ret main endp end

我的问题是为什么？ 有没有一个设置的内存地址printf使用期望找到一个参数？ 为什么打印任何东西，因为没有参数通过？

I am using printf via assembly code. I note that in the following example if I ommit the expected argument, garbage is printed.

.386 .model flat, c .stack 100h printf PROTO arg1:Ptr Byte, printlist:VARARG .data msg3fmt byte 0Ah,"%s",0Ah,"test output",0Ah,0 .code main proc INVOKE printf, ADDR msg3fmt ret main endp end

My question is why? Is there a set memory address printf uses expecting to find an argument? Why is anything printed at all since no argument is passed?

最满意答案

原因是格式说明符告诉printf应该收到多少个参数。 Printf从堆栈获取数据; 如果你没有提供任何数据，那么它会将任何发生在堆栈上的事情都视为参数。

The reason is that the format specifiers tell printf how many arguments it should have received. Printf gets its data from the stack; if you don't provide any data for it then it will pull whatever happened to be on the stack and treat as an argument.