其他的回答都很好，我不想重复他们说过的话。

One other aspect to "why enable warnings" that hasn't properly been touched on is that they help enormously with code maintenance. When you write a program of significant size, it becomes impossible to keep the whole thing in your head at once. You typically have a function or three that you're actively writing and thinking about, and perhaps a file or three on your screen that you can refer to, but the bulk of the program exists in the background somewhere and you have to trust that it keeps working.

如果你改变的某些东西给你看不见的东西带来了麻烦，你就会提醒自己。

例如Clang警告-Wswitch-enum。如果您在枚举上使用开关而漏掉了一个可能的枚举值，则会触发警告。您可能认为这是一个不太可能犯的错误:在编写switch语句时，您可能至少查看了枚举值列表。您甚至可能有一个IDE为您生成开关选项，不为人为错误留下任何空间。

六个月后，当您向枚举中添加另一个可能的条目时，这个警告才真正发挥作用。同样，如果您正在考虑所讨论的代码，那么您可能不会有问题。但是如果这个枚举用于多个不同的目的，并且它是用于您需要额外选项的其中一个目的，那么很容易忘记更新您六个月没有接触过的文件中的开关。

You can think of warnings in the same way as you'd think of automated test cases: they help you make sure that the code is sensible and doing what you need when you first write it, but they help even more to make sure that it keeps doing what you need while you prod at it. The difference is that test cases work very narrowly to the requirements of your code and you have to write them, while warnings work broadly to sensible standards for almost all code, and they're very generously supplied by the boffins who make the compilers.

非固定的警告迟早会导致代码中的错误。

例如，调试分段错误需要程序员追踪错误的根源(原因)，它通常位于代码中比最终导致分段错误的行更前面的位置。

很典型的情况是，导致错误的行是编译器发出警告而你忽略的行，而导致分段错误的行是最终抛出错误的行。

修复警告就等于修复了问题……一个经典的!

以上的演示…考虑下面的代码:

#include <stdio.h>

int main(void) {
  char* str = "Hello, World!!";
  int idx;

  // Colossal amount of code here, irrelevant to 'idx'

  printf("%c\n", str[idx]);

  return 0;
}

当使用传递给GCC的"Wextra"标志进行编译时，给出:

main.c: In function 'main':
main.c:9:21: warning: 'idx' is used uninitialized in this function [-Wuninitialized]
    9 |   printf("%c\n", str[idx]);
      |                     ^

我可以忽略它，然后执行代码……然后我就会看到一个“重大”分割错误，就像我的IP伊壁鸠鲁教授曾经说过的那样:

段错误

为了在现实场景中调试这一点，人们将从导致分段错误的行开始，并试图跟踪原因的根源是什么……他们将不得不在那里的大量代码中搜索i和str发生了什么……

直到有一天，他们发现idx使用时没有初始化，因此它有一个垃圾值，这导致索引字符串(方式)超出其界限，从而导致分割错误。

如果他们没有忽视这个警告，他们就会立即发现这个漏洞!

作为使用遗留嵌入式C代码的人，启用编译器警告有助于在提出修复时显示许多弱点和需要调查的领域。在GCC中，使用-Wall和-Wextra甚至-Wshadow变得至关重要。我不打算一一列举每一个危险，但我将列出一些已经出现的有助于显示代码问题的危险。

变量被落下

这可以很容易地指出未完成的工作和可能没有使用所有传递变量的区域，这可能是一个问题。让我们来看看一个简单的函数，它可能会触发这个:

int foo(int a, int b)
{
   int c = 0;

   if (a > 0)
   {
        return a;
   }
   return 0;
}

在没有-Wall或-Wextra的情况下编译它不会返回任何问题。-Wall会告诉你c从来不用:

foo.c:在函数' foo '中:

Foo.c:9:20:警告:未使用的变量' c ' (-Wunused-variable)

wextra还会告诉你参数b什么都不做:

foo.c:在函数' foo '中:

Foo.c:9:20:警告:未使用的变量' c ' (-Wunused-variable)

foo.c:7:20:警告:未使用参数' b ' [-Wunused-parameter] int foo(int a, int b)

全局变量阴影

这一点有点难，直到使用-Wshadow才显示出来。让我们修改上面的示例，只添加一个，但是刚好有一个全局变量和一个局部变量同名，这在尝试使用两者时造成了很多混乱。

int c = 7;

int foo(int a, int b)
{
   int c = a + b;
   return c;
}

当打开-Wshadow时，很容易发现这个问题。

Foo.c:11:9:警告:声明' c '隐藏全局声明 (-Wshadow) Foo.c:1:5:注意:阴影声明在这里

格式字符串

这在GCC中不需要任何额外的标志，但在过去它仍然是问题的根源。一个简单的函数试图打印数据，但有格式化错误，可能是这样的:

void foo(const char * str)
{
    printf("str = %d\n", str);
}

这不会打印字符串，因为格式化标志是错误的，GCC会很高兴地告诉你这可能不是你想要的:

foo.c:在函数' foo '中:

Foo.c:10:12:警告:格式' %d '期望 参数类型为' int '，但参数2的类型为' const char * ' (-Wformat =)

这只是编译器可以为您进行双重检查的许多事情中的三件。还有很多其他的方法，比如使用未初始化的变量。

其他的回答都很好，我不想重复他们说过的话。

One other aspect to "why enable warnings" that hasn't properly been touched on is that they help enormously with code maintenance. When you write a program of significant size, it becomes impossible to keep the whole thing in your head at once. You typically have a function or three that you're actively writing and thinking about, and perhaps a file or three on your screen that you can refer to, but the bulk of the program exists in the background somewhere and you have to trust that it keeps working.

如果你改变的某些东西给你看不见的东西带来了麻烦，你就会提醒自己。

例如Clang警告-Wswitch-enum。如果您在枚举上使用开关而漏掉了一个可能的枚举值，则会触发警告。您可能认为这是一个不太可能犯的错误:在编写switch语句时，您可能至少查看了枚举值列表。您甚至可能有一个IDE为您生成开关选项，不为人为错误留下任何空间。

六个月后，当您向枚举中添加另一个可能的条目时，这个警告才真正发挥作用。同样，如果您正在考虑所讨论的代码，那么您可能不会有问题。但是如果这个枚举用于多个不同的目的，并且它是用于您需要额外选项的其中一个目的，那么很容易忘记更新您六个月没有接触过的文件中的开关。

You can think of warnings in the same way as you'd think of automated test cases: they help you make sure that the code is sensible and doing what you need when you first write it, but they help even more to make sure that it keeps doing what you need while you prod at it. The difference is that test cases work very narrowly to the requirements of your code and you have to write them, while warnings work broadly to sensible standards for almost all code, and they're very generously supplied by the boffins who make the compilers.

为什么要启用警告?

众所周知，C和c++编译器在默认情况下不擅长报告一些常见的程序员错误，例如:

忘记初始化变量 忘记从函数返回值 printf和scanf族中的参数与格式字符串不匹配 函数的使用没有事先声明(仅限C语言)

这些可以被检测和报告，只是通常不是默认情况;此特性必须通过编译器选项显式地请求。

如何启用警告?

这取决于你的编译器。

微软C和c++编译器理解/W1、/W2、/W3、/W4和/Wall这样的开关。至少使用/W3。/W4和/Wall可能会对系统头文件发出错误的警告，但如果您的项目使用这些选项之一进行了干净的编译，那么就使用它。这些选择是相互排斥的。

大多数其他编译器都理解-Wall、-Wpedantic和-Wextra这样的选项。-Wall是必要的，其余的都是推荐的(注意，尽管它的名字，-Wall只启用最重要的警告，而不是全部)。这些选项可以单独使用，也可以一起使用。

您的IDE可能有办法从用户界面启用这些功能。

为什么我要把警告当作错误?它们只是警告!

A compiler warning signals a potentially serious problem in your code. The problems listed above are almost always fatal; others may or may not be, but you want compilation to fail even if it turns out to be a false alarm. Investigate each warning, find the root cause, and fix it. In the case of a false alarm, work around it — that is, use a different language feature or construct so that the warning is no longer triggered. If this proves to be very hard, disable that particular warning on a case by case basis.

你不希望只是把警告作为警告，即使它们都是假警报。对于发出的警告总数小于7的非常小的项目来说，这是可行的。再多一点，新的警告就很容易淹没在大量熟悉的旧警告中。不要允许这种情况发生。只是让你所有的项目编译干净。

Note this applies to program development. If you are releasing your project to the world in the source form, then it might be a good idea not to supply -Werror or equivalent in your released build script. People might try to build your project with a different version of the compiler, or with a different compiler altogether, which may have a different set of warnings enabled. You may want their build to succeed. It is still a good idea to keep the warnings enabled, so that people who see warning messages could send you bug reports or patches.

如何将警告视为错误?

这同样是通过编译器开关完成的。/WX是微软的，大多数其他人使用-Werror。在这两种情况下，如果产生任何警告，编译都会失败。

这就够了吗?

可能不是!随着优化级别的提高，编译器开始越来越仔细地检查代码，而这种仔细检查可能会发现更多的错误。因此，不要满足于警告开关本身，总是使用它们时，编译优化启用(-O2或-O3，或/O2如果使用MSVC)。

众所周知，就hll而言，C是一种相当低级的语言。虽然c++看起来是一种比C高级得多的语言，但它仍然具有C的一些特征。其中一个特点就是这些语言是由程序员设计的，为程序员设计的——特别是那些知道自己在做什么的程序员。

(对于这个答案的其余部分，我将专注于C。我要说的大部分内容也适用于c++，尽管可能没有那么强烈。尽管Bjarne Stroustrup有一句名言:“C很容易搬起石头砸自己的脚;c++让它变得更难，但当你这样做的时候，它会把你的整条腿都炸掉。”)

如果你知道你在做什么——真的知道你在做什么——有时候你可能不得不“打破规则”。但大多数时候，我们大多数人都会同意，善意的规则让我们所有人都远离麻烦，一直肆意违反这些规则是一个坏主意。

But in C and C++, there are surprisingly large numbers of things you can do that are "bad ideas", but which aren't formally "against the rules". Sometimes they're a bad idea some of the time (but might be defensible other times); sometimes they're a bad idea virtually all of the time. But the tradition has always been not to warn about these things — because, again, the assumption is that programmers know what they are doing, they wouldn't be doing these things without a good reason, and they'd be annoyed by a bunch of unnecessary warnings.

当然，并不是所有的程序员都知道自己在做什么。特别是，每个C程序员(无论多么有经验)都要经历一个开始C程序员的阶段。即使是有经验的C程序员也会粗心大意，犯错误。

最后，经验表明，程序员不仅会犯错误，而且这些错误会产生真正的、严重的后果。如果你犯了一个错误，编译器没有警告你，而且程序没有立即崩溃，或者因为它而做一些明显的错误，这个错误可能潜伏在那里，隐藏，有时长达数年，直到它造成一个真正的大问题。

So it turns out that, most of the time, warnings are a good idea, after all. Even the experienced programmers have learned that (actually, it's "especially the experienced programmers have learned that"), on balance, the warnings tend to do more good than harm. For every time you did something wrong deliberately and the warning was a nuisance, there are probably at least ten times you did something wrong by accident and the warning saved you from further trouble. And most warnings can be disabled or worked around for those few times when you really want to do the "wrong" thing.

(这类“错误”的一个经典例子是if(A = b)的测试。大多数时候，这确实是一个错误，所以现在大多数编译器都会对此发出警告——有些甚至是默认的。但是如果你真的想把b赋值给a并测试结果，你可以通过输入if((a = b))来禁用警告。

The second question is, why would you want to ask the compiler to treat warnings as errors? I'd say it's because of human nature, specifically, the all-too-easy reaction of saying "Oh, that's just a warning, that's not so important, I'll clean that up later." But if you're a procrastinator (and I don't know about you, but I'm a world-class procrastinator) it's easy to put off the necessary cleanup for basically ever — and if you get into the habit of ignoring warnings, it gets easier and easier to miss an important warning message that's sitting there, unnoticed, in the midst of all the ones you're relentlessly ignoring.

因此，要求编译器将警告视为错误是你可以对自己玩的一个小技巧，以避免这个人类的弱点，迫使自己立即修复警告，否则你的程序将无法编译。

Personally, I'm not as insistent about treating warnings as errors — in fact, if I'm honest, I can say that I don't tend to enable that option in my "personal" programming. But you can be sure I've got that option enabled at work, where our style guide (which I wrote) mandates its use. And I would say — I suspect most professional programmers would say — that any shop that doesn't treat warnings as errors in C is behaving irresponsibly, is not adhering to commonly-accepted industry best practices.