从C ++调用NSLog：“格式字符串不是字符串字面量（可能不安全）”。 [英] Calling NSLog from C++: "Format string is not a string literal (potentially insecure)"

问题描述

当我从C ++调用NSLog时，Xcode抱怨传递给NSLog的格式字符串不是文字字符串。这是一行代码触发警告：

When I call NSLog from C++, Xcode complains that the format string passed to NSLog is not a literal string. Here's a line of code that triggers the warning:

NSLog(CFSTR("Leaking?"));

我不知道有任何方法来编写一个字面量的NSString在C + +，看到相关的警告，我可以在项目设置中关闭。有没有办法从C ++调用NSLog不触发此消息？我使用Xcode 4.2.1。

I'm not aware of any way to code a literal NSString in C++, and I don't see a relevant warning I can turn off in the project settings. Is there a way to call NSLog from C++ without triggering this message? I'm using Xcode 4.2.1.

编辑：这真的是C ++代码。我通常避免使用Objective-C ++，坚持Objective-C或普通的老C ++，因为没有关于什么在Objective-C + +什么工作的官方文档和什么不。我只发现了模糊的警告，（例如）STL的某些部分可能有问题。我使用模板，STL和C ++的其他高级功能，所以我想要安全。

This really is C++ code. I usually avoid Objective-C++, sticking to either Objective-C or plain old C++, because there's no official documentation about what works in Objective-C++ and what doesn't. I've only found vague warnings that (for example) there may be issues with some parts of the STL. I use templates, the STL, and other "advanced" features of C++, so I want to play it safe.

编辑＃2，解决方案： clang支持比实际记录的更多的警告标志。 （应该从Xcode提供给我的警告长列表中显而易见。）我尝试了-Wno格式非线性a gcc，现在Xcode是快乐的。

Edit #2, the solution: I just figured out clang supports a lot more warning flags than are actually documented. (It should have been obvious from the long list of warnings that Xcode offered me.) I tried -Wno-format-nonliteral a la gcc, and now Xcode is happy.

推荐答案

所有你需要做的是写 @this创建一个文本NSString对象。

All you have to do is write @"this" to create a literal NSString object.

那么用 NSLog（@Leaking？）; 应该很好。

您可能需要使用扩展名 .mm 重命名文件，以确保它已编译作为Objective-C ++（Objective-C和C ++的突变爱情孩子）。如果你不想这样做，你可以在一个小的mm文件中调用NSLog，然后从你的C ++代码调用该函数。它看起来像这样：

You might have to rename your file with the extension .mm to make sure it is compiled as Objective-C++ (the mutant love-child of Objective-C and C++). If you don't want to do that, you could make a wrapper function in a tiny mm file that calls NSLog, and then call that function from your C++ code. It would look like this:

void MyNSLog(const char *message)
{
    NSLog(@"%s", message);
}

请注意，编译器给你的悲伤的原因是，不可变的字符串文字（其中内容在编译时是已知的）是一种安全风险。否则，可以将格式字符串更改为包含不存在的参数的格式说明符（例如，％d ）。如果发生这种情况，NSLog将只是从堆栈获取随机指针，可能会发生不良。 （有关详情，请参见此问题。 ）

Note that the reason the compiler is giving you grief is that using anything but an immutable string literal (where the contents are known at compile time) is a security risk. Otherwise, the format string could be changed to include format specifiers (e.g., %d) for parameters that aren't there. If that happened, NSLog would just get random pointers from the stack and something bad could happen. (See this question for more info.)

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