我可以在同一个项目 (Visual Studio 19) 中有多个 C 源文件吗？

Question

Beginner here. I code in C atm. So Ive just started using VS 2019. A few troubles along the way but I got Build error along with LNK 2005 and LNK 1169. Turns out I cant have multiple files in the same project. Especially if Im using same header in the files. In this case it was stdio.h and math.h. I recreated this multiple times. The code would compile without a hitch only if one file was present in the project. Or atleast just one file with that particular header. Which pretty much prevents me from having multiple C source files under the same project. So is there any way to have multiple files in the same project without these errors.

A little annoying that I can't have multiple files with same header which is impossible cause obviously, I gotta use stdio.h everywhere. enter image description here

Answer 1

Essentially a Solution is a container used to contain multiple Projects , you can choose to compile either the whole Solution (so all the projects in the solution), or a single Project in said Solution.

Each Project can have only 1 main() because otherwise your OS won't know where to start executing, of course you can have multiple source files in the same project otherwise for even smaller projects you'd have a single file with a huge number of lines. This structure is quite common in many IDE s (maybe with different names than Project and Solution , this is just a nomenclature that VS uses), it isn't really bound to Windows or Linux in particular.

Try on Linux to have multiple source files with multiple main() and try to compile then together with gcc , you'll see that you get a very similar error.

You also can't have the same function definition in multiple files otherwise you get the LNK 2005 linker error that you've seen. This is because when the Linker is linking your files if it finds two identical definitions it doesn't know which one to take and goes crazy.

But then how do you include the same header files in different sources?

Well that's why .h files have include guards , they ensure that the contents of an .h files are included by the linker only once in each Compilation.

Usually in the header file there is one of two possible ways to include these guards, there are very small differences between these two methods but they don't really apply if you're not doing some very specific stuff:

 #pragma once
 // Content of the header

or

#ifndef GUARD_H
#define GUARD_H

// Content of header

#endif

Where GUARD_H should be different for every .h file, usually it's a combination of your Project and header file names just to make sure it's different to other guards that could exist in other headers.

That's also why you can't (and shouldn't) include Source files in your code, if you include a source file then you are at a high risk of including the same definition multiple times since they don't use include guards.

The C file gets stored normally in any folder you want and gets compiled with a gcc and ./a.out in the terminal

That's essentially what VS does, just instead of you choosing which files to add in the compilation VS takes automatically all the files in the same Solution or Project (depending which one you decide to build).

For convenience, if you are just starting to learn, create a new solution for each Project (so for every main() ) that you want.

Is this better or worse than using a simple text editor? Well, after the first 10-15 minutes of learning you'll see that it's much faster and useful to use an actual IDE as it provides many features that will make you write code faster and with less errors.

This is a really quick explanation of how things work in general. If you can, try to find someone IRL that can explain these things to you. It's really hard to explain it on the internet but it will take less than 10 minutes being together in front of the same computer.