C++ 为什么 g++ 找不到 iostream.h？

Why can't g++ find iostream.h?

提问by quakkels

I'm trying to understand how to compile C++ programs from the command line using g++ and (eventually) Clang on Ubuntu.

我试图了解如何在 Ubuntu 上使用 g++ 和（最终）Clang 从命令行编译 C++ 程序。

I found a webpage which explains MakeFiles and I am following their directions. http://mrbook.org/tutorials/make/

我找到了一个解释 MakeFiles 的网页，我正在按照他们的指示进行操作。http://mrbook.org/tutorials/make/

I downloaded the four example files into their own directory.

我将四个示例文件下载到它们自己的目录中。

• main.cpp
• hello.cpp
• factorial.cpp
• functions.h

• 主程序
• 你好.cpp
• 阶乘文件
• 函数.h

I then went ahead and ran their example of how to manually compile without a MakeFile.

然后我继续运行他们的示例，说明如何在没有 MakeFile 的情况下手动编译。

g++ main.cpp hello.cpp factorial.cpp -o hello

When I ran the command from above, I received the following error from g++:

当我从上面运行命令时，我从 g++ 收到以下错误：

main.cpp:1:22: fatal error: iostream.h: No such file or directory
compilation terminated.
hello.cpp:1:22: fatal error: iostream.h: No such file or directory
compilation terminated.

My only experience with writing c++ is using an IDE such as VS C++ Express or CodeBlocks. Isn't the compiler supposed to know what iostream.h is and where to find it?

我编写 C++ 的唯一经验是使用 IDE，例如 VS C++ Express 或 CodeBlocks。编译器不应该知道 iostream.h 是什么以及在哪里可以找到它吗？

How do I get rid of this error so the program willl compile?

我如何摆脱这个错误以便程序能够编译？

Thanks for any help.

谢谢你的帮助。

回答by Adam Rosenfield

Before the C++ language was standardized by the ISO, the header file was named <iostream.h>, but when the C++98 standard was released, it was renamed to just <iostream>(without the .h). Change the code to use #include <iostream>instead and it should compile.

在 C++ 语言被 ISO 标准化之前，头文件被命名为<iostream.h>，但是当 C++98 标准发布时，它被重命名为 just <iostream>（没有.h）。更改要使用的代码#include <iostream>，它应该可以编译。

You'll also need to add a using namespace std;statement to each source file (or prefix each reference to an iostream function/object with a std::specifier), since namespaces did not exist in the pre-standardized C++. C++98 put the standard library functions and objects inside the stdnamespace.

您还需要向using namespace std;每个源文件添加一条语句（或使用std::说明符为每个对 iostream 函数/对象的引用添加前缀），因为在预标准化的 C++ 中不存在命名空间。C++98 将标准库函数和对象放在std命名空间内。

回答by Cheers and hth. - Alf

<iostream.h>has never been a standard C++ header, because it did not make it into the C++ standard.

<iostream.h>从来都不是标准的 C++ 头文件，因为它没有进入 C++ 标准。

Instead we got <iostream>, in 1998.

相反，我们<iostream>在 1998 年得到了。

Steer well clear of teaching material using non-standard stuff such as <iostream.h>or void main.

避免使用非标准内容（例如<iostream.h>或 ）的教材void main。

However, as a practical solution for your current pre-standard code, you may try to replace

但是，作为当前预标准代码的实用解决方案，您可以尝试替换

#include <iostream.h>

with

和

#include <iostream>
using namespace std;

It’s not guaranteed to work, but chances are that it will work.

它不能保证工作，但有可能它会工作。

回答by nodlehs

Another related issue that wasn't mentioned here, so I will include it for anyone's future reference, is from the command line the compiler needs the environment path variable updated to find the location of the c++ header files. In windows you can just update the path environment using the 'advanced system properties' GUI and add the location of the c++ include files. This will update the PATH environment variable in Windows cmd & Cygwin automatically upon restarting the shell.

此处未提及的另一个相关问题，因此我会将其包含在内以供将来参考，即从命令行编译器需要更新环境路径变量以查找 c++ 头文件的位置。在 Windows 中，您可以使用“高级系统属性”GUI 更新路径环境并添加 c++ 包含文件的位置。这将在重新启动 shell 时自动更新 Windows cmd 和 Cygwin 中的 PATH 环境变量。

To update your PATH from Linux or the Cygwin shell type... PATH=$PATH:/your_path_here Example:PATH=$PATH:/cygdrive/c/cygwin/lib/gcc/i686-pc-mingw32/4.7.3/include/c++ Also a good idea to add just the include directory as well: PATH=$PATH:/cygdrive/c/cygwin/lib/gcc/i686-pc-mingw32/4.7.3/include/ ...or check the proper directories for the location of your installation's include files, I recommend installing mingw for use with Cygwin, which is envoked with g++.

要从 Linux 或 Cygwin shell 类型更新 PATH... PATH=$PATH:/your_path_here 示例：PATH=$PATH:/cygdrive/c/cygwin/lib/gcc/i686-pc-mingw32/4.7.3/include /c++ 也是一个好主意，只添加包含目录：PATH=$PATH:/cygdrive/c/cygwin/lib/gcc/i686-pc-mingw32/4.7.3/include/ ...或检查正确的安装包含文件的位置的目录，我建议安装 mingw 以与 Cygwin 一起使用，它是用 g++ 调用的。

To install additional needed packages in Cygwin re-run the Cygwin install utility & check install from Internet to add packages from web repositories and add mingw-gcc-g++ & mingw-binutils. To compile: g++ hello.cpp -o hello

要在 Cygwin 中安装其他需要的软件包，请重新运行 Cygwin 安装实用程序并检查从 Internet 安装以从 Web 存储库添加软件包并添加 mingw-gcc-g++ 和 mingw-binutils。编译：g++ hello.cpp -o hello

If using the gcc utility instead compile with the command: gcc hello.cpp -o hello -lstdc++ ... to get your executable.

如果使用 gcc 实用程序而不是使用以下命令编译： gcc hello.cpp -o hello -lstdc++ ... 以获取您的可执行文件。

As long as you have either gcc or mingw installed and the path to the c++ include files is in your path environment variable, the commands will work.

只要您安装了 gcc 或 mingw 并且 C++ 包含文件的路径在您的路径环境变量中，这些命令就会起作用。