scanf / fgets do not block for input in C wasm kernel (stdin unsupported)

[anutosh491]

VS

the C++ wasm kernel

[anutosh491]

cc @davy39 just brining to your attention

[dannluciano]

@davy39 and @anutosh491 the problem is because the C language has stdin very close with Operate System and File System.

I think that we have overwritten the scanf, getline, getchar functions with something like this in src/main_emscripten_kernel.cpp

#include <cstdio>
#include <cstdarg>
#include <string>
#include <iostream>

#include <xeus/xinput.hpp> 

extern "C" {

int xscanf(const char* format, ...)
{
    std::string input = xeus::blocking_input_request("", false);
    if (input.empty()) return EOF;

    if (input.back() != '\n') input.push_back('\n');

    const char* tmp = "/tmp/stdin_xscanf.txt";
    FILE* f = fopen(tmp, "w");
    if (!f) return EOF;
    fputs(input.c_str(), f);
    fclose(f);

    FILE* fin = freopen(tmp, "r", stdin);
    if (!fin) return EOF;

    va_list args;
    va_start(args, format);
    int r = vfscanf(stdin, format, args);
    va_end(args);

    return r;
}

int xgetchar()
{
    std::string input = xeus::blocking_input_request("", false);
    if (input.empty()) return EOF;
    return (unsigned char)input[0];
}

} 

#define scanf(...)   xscanf(__VA_ARGS__)
#define getchar()    xgetchar()

Can someone guide me on this?

[anutosh491]

Hmm,

I'll have a go at this issue soon.

I just started comparing some file operations and fortunately that works

like the C++ kernel

[dannluciano]

Today in my classes I use the %%file magic command to create an input file and use fscanf. It not the same of scanf but close.

%%file input.txt
John Doe

#include <stdio.h>
int main(void){
    FILE* in = fopen("input.txt", "r");
    
    printf("Hello World\n");
    char name[255] = {"Fulano"};
    fscanf(in, "%255[^\n]", name);
    printf("God job: %s\n", name);
    
    fclose(in);
}