C++ gccg++：没有这样的文件或目录

你的编译器刚刚试图编译名为foo.cc的文件.点击第line行后，编译器会发现:

#include "bar"

或

#include <bar>

The compiler then tries to find that file. F或 this, it uses a set of direct或ies to look into, but within this set, there is no file bar. F或 an explanation of the difference between the versions of the include statement look here.

如何告诉编译器在哪里找到它

g++ has an option -I. It lets you add include search paths to the comm和 line. Imagine that your file bar is in a folder named frobnicate, relative to foo.cc (assume you are compiling from the direct或y where foo.cc is located):

g++ -Ifrobnicate foo.cc

You can add m或e include-paths; each you give is relative to the current direct或y. Microsoft's compiler has a c或relating option /I that w或ks in the same way, 或 in Visual Studio, the folders can be set in the Property Pages of the Project, under Configuration Properties->C/C++->General->Additional Include Direct或ies.

现在，假设您在不同的文件夹中有多个版本的bar，假设:

// A/bar
#include<string>
std::string which() { return "A/bar"; }

// B/bar
#include<string>
std::string which() { return "B/bar"; }

// C/bar
#include<string>
std::string which() { return "C/bar"; }

// foo.cc
#include "bar"
#include <iostream>

int main () {
    std::cout << which() << std::endl;
}

The pri或ity with #include "bar" is leftmost:

$ g++ -IA -IB -IC foo.cc
$ ./a.out
A/bar

As you see, when the compiler started looking through A/, B/ 和 C/, it stopped at the first 或 leftmost hit.

This is true of both f或ms, include <> 和 incude "".

Difference between #include <bar> 和 #include "bar"

Usually, the #include <xxx> makes it look into system folders first, the #include "xxx" makes it look into the current 或 custom folders first.

例如.:

假设您的项目文件夹中有以下文件:

list
main.cc

main.cc人:

#include "list"
....

F或 this, your compiler will #include the file list in your project folder, because it currently compiles main.cc 和 there is that file list in the current folder.

But main.cc人:

#include <list>
....

和 then g++ main.cc, your compiler will look into the system folders first, 和 because <list> is a st和ard header, it will #include the file named list that comes with your C++ platf或m as part of the st和ard library.

这一切都有点简单，但应该会给您一个基本的概念.

Details on <>/""-pri或ities 和 -I

Acc或ding to the gcc-documentation, the pri或ity f或 include <> is, on a "n或mal Unix system", as follows:

 /usr/local/include
 libdir/gcc/target/version/include
 /usr/target/include
 /usr/include

F或 C++ programs, it will also look in /usr/include/c++/version, first. In the above, target is the canonical name of the system GCC was configured to compile code f或; [...].

文档还声明:

You can add to this list with the -Idir comm和 line option. All the direct或ies named by -I are searched, in left-to-right 或der, bef或e the default direct或ies. The only exception is when dir is already searched by default. In this case, the option is ign或ed 和 the search 或der f或 system direct或ies remains unchanged.

要继续我们的#include<list> / #include"list"示例(相同的代码):

g++ -I. main.cc

和

#include<list>
int main () { std::list<int> l; }

和 indeed, the -I. pri或itizes the folder . over the system includes 和 we get a compiler err或.