在变量自己的声明中将变量分配给自身
#include <stdio.h>
int main() {
int c = c;
printf("c is %i\n", c);
return 0;
}
我正在定义一个名为 c 的整数变量，并将其值分配给自身。但这怎么能编译呢？ c 还没有初始化，那么如何将它的值赋给自己呢？当我运行该程序时，我得到c is 0。
我假设编译器正在生成为 c 变量分配空间的汇编代码（当编译器遇到 int c 语句时）。然后，它获取未初始化空间中的任何垃圾值并将其分配回c。这是正在发生的事情吗？
#include <stdio.h>
int main() {
int c = c;
printf("c is %i\n", c);
return 0;
}
I'm defining an integer variable called c, and I'm assigning its value to itself. But how can this even compile? c hasn't been initialized, so how can its value be assigned to itself? When I run the program, I get c is 0.
I am assuming that the compiler is generating assembly code that is assigning space for the the c variable (when the compiler encounters the int c statement). Then it takes whatever junk value is in that un-initialized space and assigns it back to c. Is this what's happening?
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我记得在之前的回答中引用过这一点，但现在找不到。
C++03 §3.3.1/1：
因此变量 c 即使在初始化程序部分之前也是可用的。
编辑：抱歉，您专门询问了有关 C 的问题；虽然我确信那里有一条等效的线。詹姆斯·麦克内利斯发现了它：
I remember quoting this in a previous answer but I can't find it at the moment.
C++03 §3.3.1/1:
Therefore the variable c is usable even before the initializer part.
Edit: Sorry, you asked about C specifically; though I'm sure there is an equivalent line in there. James McNellis found it:
你的猜测完全正确。
int c将变量的空间压入堆栈，然后读取该变量并将其重写为c = c部分（尽管编译器可能会对其进行优化） 。您的编译器将值推送为0，但并不保证始终如此。Your guess is exactly right.
int cpushes space onto the stack for the variable, which is then read from and re-written to for thec = cpart (although the compiler may optimize that out). Your compiler is pushing the value on as0, but this isn't guaranteed to always be the case.使用未初始化的值是未定义的行为（§C99 J.2“具有自动存储持续时间的对象的值在其被使用时被使用”
不确定”）。所以从 鼻恶魔 到 c = 任何事情都可能发生0，到玩 Nethack。
It's undefined behavior to use an uninitialized value (§C99 J.2 "The value of an object with automatic storage duration is used while it is
indeterminate"). So anything can happen from nasal demons to c = 0, to playing Nethack.
C 规范不保证变量将被初始化为 0、0.0 或“”或“”。
这是编译器的一个功能，您永远不必强迫它发生。
我总是将我的 IDE/编译器设置为对此发出警告。
The C specification don't assure that variables will be initialized to 0, 0.0 nor "" or ''.
That is a feature of compilers and never you must thrust that will happen.
I always set my IDE/Compiler to warning about that.
c已经初始化了！
虽然这是一行代码，但实际上是先初始化c，然后给c赋值。你很幸运，编译器为你将 c 初始化为零。
c has been initialized!
Although this is one line of code, it is in fact initializing c first, then assigning c to it. You are just lucky that the compiler is initializing c to zero for you.