cannot debug C program reading large file from stdin on macOS 12.6 Monterey

Environment

• OS and version: macOS 12.6 Monterey
• VS Code: 1.72.2
• C/C++ extension: unsure, but downloaded approx. Oct. 28 2022
• OS and version of remote machine (if applicable):n/a
• GDB / LLDB version: lldb-1400.0.30.3

Bug Summary and Steps to Reproduce

Bug Summary:

I have been unable to find a way to connect large datasets to the stdin of a C code program being debugged by vscode -- it seems possible only to use the launch.json "externalConsole": true setting to input small amounts of manually entered input via an opened terminal window. (Such manual input is entirely unsuited to debugging a program with very large multi-column numerical input datasets.) This problem occurs on both Intel and Apple M1 macOS 12.6 systems.

I have seen recommendations in various places to use a launch.json args setting for this, e.g., "args": ["<", "/tmp/somefile"] , but this simply does not work (other than to corrupt the program's main() argv[] array by appending spurious < and /tmp/somefile arguments, which should obviously not be visible to any program actually reading stdin ). Here is the launch.json entry I tried unsuccessfully to use:

        {
            "name": "vscstdio-stdin-test",
            "type": "cppdbg",
            "request": "launch",
            "program": "${workspaceFolder}/vscstdio",
            "args": ["<", "/etc/group"],
            "stopAtEntry": false,
            "cwd": "${fileDirname}",
            "environment": [],
            "externalConsole": false,
            "MIMode": "lldb"
        }

(Note that specifying "externalConsole": true in that configuration only improved the situation to the extent of allowing manually typed input to be sent to stdin , which is not sufficient for my purposes.)

Here is a small sample program which demonstrates the problem. It simply prints out the contents of the main() argv[] array, including the spurious < and /etc/group arguments, and then echoes to stdout whatever is read from stdin :

#include <stdio.h>
#include <stdlib.h>
    
char buf[512];

int main(int argc, char **argv) {       
        int i;
            
        for (i= 0; i < argc; i++)
                (void) fprintf(stderr, "%1d: %s\n", i, argv[i]);
        (void) fflush(stderr);
            
        for (i= 0; fgets(buf, (int) 512, stdin) != (char *) 0; i++)
                (void) fprintf(stdout, "[%3d] _%s", i, buf);

        (void) fprintf(stdout, "At EOF\n");
        
        exit(0);
}

When run with the above launch.json configuration it hangs indefinitely on the first call to fgets() instead of properly reading the redirected /etc/group through stdin .

I truly hope you can either fix this problem or tell me what I am doing wrong, otherwise vscode is not usable to me for debugging a lot of my project's software which makes heavy use of stdio. Thanks!

Debugger Configurations

See launch.json above.

tasks.json:
{
    "tasks": [
        {
            "type": "cppbuild",
            "label": "C/C++: clang build active file",
            "command": "/usr/bin/clang",
            "args": [
                "-fcolor-diagnostics",
                "-fansi-escape-codes",
                "-g",
                "${file}",
                "-o",
                "${fileDirname}/${fileBasenameNoExtension}"
            ],
            "options": {
                "cwd": "${fileDirname}"
            },
            "problemMatcher": [
                "$gcc"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            },
            "detail": "Task generated by Debugger."
        }
    ],
    "version": "2.0.0"
}

Debugger Logs

None.

Other Extensions

No response

Additional Information

No response

Start with the launch.json cppdbg configuration and the sample C program; compare the externalConsole and args settings while reproducing the hang with /etc/group as stdin. Check how the extension launches LLDB on macOS 12.6. Done means file input reaches stdin without adding redirection tokens to argv or blocking at fgets().