C++ vs C

int pty_getproc(lua_State* L)
{
    int fd = lua_tonumber(L, 1);

    pid_t pgrp = tcgetpgrp(fd);
    if (pgrp == -1)
        return lua_return(L, nullptr, "failed to locate pid from fd");

    std::ifstream ifs("/proc/" + std::to_string(pgrp) + "/cmdline");

    if(!ifs.is_open())
        return lua_return(L, nullptr, "failed to open /proc/" + std::to_string(pgrp) + "/cmdline");

    std::string contents;
    ifs >> contents;
    ifs.close();

    lua_pushstring(L, contents.c_str());
    return 1;
}

int c_pty_getproc(lua_State* L)
{
    int fd = lua_tonumber(L, 1);

    FILE *f;
    char *path, *buf;
    size_t len;
    int ch;
    pid_t pgrp;
    int r;

    if ((pgrp = tcgetpgrp(fd)) == -1)
        return lua_return(L, nullptr, "failed to locate pid from fd");

    r = asprintf(&path, "/proc/%lld/cmdline", (long long)pgrp);
    if (r == -1 || path == NULL)
        return lua_return(L, nullptr, "failed to open /proc/$pid/cmdline");

    if ((f = fopen(path, "r")) == NULL)
    {
        free(path);
        return lua_return(L, nullptr, "failed to open /proc/$pid/cmdline");
    }

    free(path);

    len = 0;
    buf = NULL;
    while ((ch = fgetc(f)) != EOF) {
        if (ch == '\0') break;
        buf = (char *)realloc(buf, len + 2);
        if (buf == NULL) return lua_return(L, nullptr, "failed to read file");
        buf[len++] = ch;
    }

    if (buf != NULL) {
        buf[len] = '\0';
    }

    fclose(f);

    lua_pushstring(L, buf);
    return 1;
}