After c++ is compiled into wasm, the internal methods are not found and need to be imported by “imports”

[GarasChan]

C++ Code：

#include <iostream>
using namespace std;

extern "C" {
    void ReadHead(char *path)
    {
        if ((m_ShpFile_fp = fopen(path, "rb")) == NULL)
        {
            return;
        }
        fread(&file_Head.FileCode, sizeof(int), 1, m_ShpFile_fp);
        fread(&file_Head.FileLength, sizeof(int), 1, m_ShpFile_fp);
        file_Head.FileLength = OnChangeByteOrder(file_Head.FileLength);
        fread(&file_Head.ShapeType, sizeof(int), 1, m_ShpFile_fp);
        ...
    }
}

here, the functions "fopen" and "fread" can not be found。

emcc：
emcc shp.cpp -Os -s WASM=1 -s SIDE_MODULE=1 -o shp.wasm

wasm file：

...
(import "env" "_fopen" (func $env._fopen (type $t0)))
(import "env" "_fread" (func $env._fread (type $t8)))
...

Error：

• Uncaught (in promise) LinkError: Import GHC output: TypeError: Cannot read property 'tokens' #1 module="env" function="_fopen" error: function import requires a callable at fetch.then.then.then.module (http://127.0.0.1:5500/index.html:126:36)
• Uncaught (in promise) LinkError: Import GHC output: TypeError: Cannot read property 'tokens' #1 module="env" function="_fread" error: function import requires a callable at fetch.then.then.then.module (http://127.0.0.1:5500/index.html:126:36)

Here are some of the errors listed. I think it may be that emcc compiles without introducing the required lib, which is the header file (.h).

[kripken]

In a side module, system libraries are not linked in, so it calls out to things like fopen etc. And then you need to provide them as imports. (A main module will provide them to the side module; if you load the module yourself, you need to handle it.)

[GarasChan]

Thank you very much for your reply. And how to import the required resources? @kripken

[kripken]

You can look at a main module to see how it does it (compile it, run it to see that it works, then look at the code). There isn't much more in terms of docs for this - some of it is the normal libc API, some is internal APIs.

[GarasChan]

Where is the main module, and how to find it? @kripken

[kripken]

See https://github.com/kripken/emscripten/wiki/Linking

[GarasChan]

Thanks for your help very much, and I will close this case. @kripken