AW: [std-proposals] std::argc std::argv (available to global constructors)

This is being pursued as WG14 N2948 (Accessing the command line arguments outside of main()).
Tom.
On 6/13/23 7:02 AM, Frederick Virchanza Gotham via Std-Proposals wrote:
[ I tried to put this up on GodBolt and provide a link,   but I gave up on the GNU inline assembler syntax,   I just couldn't get it to work ]  Ever since C++ came out in 1979, there hasn't been any good reason why the command line arguments to a program cannot be used as arguments to the constructors of global objects.  I propose that in <cstdlib>, there will be:      namespace std {         extern int argc;         extern char **argv;     }  To implement this in my following example, the entry point to the program will be 'entrypoint' instead of '_start', and the values of 'argc' and 'argv' will be gotten from the stack. The following syntax is for the 'nasm' assembler:      extern _ZSt4argc    ; mangled name of std::argc (dword = 4 bytes)     extern _ZSt4argv    ; mangled name of std::argv (qword = 8 bytes)     extern _start      section .text         global entrypoint:function         entrypoint:             push r15      ; callee-saved (we will restore it later)              add rsp, 8    ; move the stack pointer to argc             mov r15d, dword[rsp]             mov dword[_ZSt4argc], r15d              add rsp, 8    ; move the stack pointer to argv             mov r15, rsp             mov qword[_ZSt4argv], r15              sub rsp, 16   ; move the stack pointer back to where we stored r15             pop r15    ; restore the original value of r15 (callee-saved)             jmp _start  So you compile this assembler as follows:      nasm -o entrypoint.o -f elf64 entrypoint.asm  And then we build our program with:      g++ -o prog main.cpp -no-pie entrypoint.o -e entrypoint  Here's an example program that works:      #include <iostream>      namespace std {         int argc;         char **argv;     }      class LaserController {         int const grade;         char model[16u];     public:         LaserController(int const arg_grade, char const *const arg_model)           : grade(arg_grade)         {             if ( nullptr == arg_model ) { model[0u] = '\0'; return; }              for ( unsigned i = 0u; i < sizeof(model); ++i )             {                 model[i] = arg_model[i];                 if ( '\0' == model[i] ) break;             }              model[sizeof(model) - 1u] = '\0';         }          void Print(void)         {             std::cout << "Grade: " << grade << ", Model: " << model << std::endl;         }     };      LaserController gLaser( std::argc, std::argv[ std::argc - 1u ] );      int main(int argc, char **argv)     {         gLaser.Print();     }