Is C++ platform dependent?

Question

Can we say that C++ is platform dependent?

I know that C++ uses compiler, and those compiler are different for different platforms. When we compile C++ code using compiler for example: on Windows, .EXE format file created.

Why is an .EXE file OS/Platform dependent?

What is the format inside .EXE files?

Why can't we run it on other platforms?

Answer 1

This is actually a relatively extensive topic. For simplicity, it comes down to two things: operating system and CPU architecture.

First of all, *.exe is generally only Windows since it is binary code which the windows operating system knows how to execute. Furthermore, the operating system knows how to translate this to the proper code for the architecture (this is why Windows is "just compatible"). Note that a lot more is going on, but this is a (very) high-level abstraction of what is going on.

Now, compilers will take C++ code and generate its corresponding assembly code for the architecture (i.e. x86, MIPS, etc.). Usually the compiler also has an assembler (or one which it can rely on). The assembler the links code and generates binary code which the hardware can execute. For more information on this topic look for more information on co-generation.

Additional Note

Consider Java which is not platform-dependent. Java compilers generate Java bytecode which is run on the Java virtual machine (JVM). It is important to notice that any time you wish to run a Java application you must run the Java virtual machine. Since the precompiled JVM knows how to operate on your operating system and CPU architecture, it can run its Java bytecode and effectively run the corresponding actions for your particular system.

In a compiled binary file (i.e. one from C++ code), you have system bytecode. So the kind of instructions which Java simulates for you are directly hard-coded into the .exe or whatever binary format you are using. Consider the following example:

Notice that this java code must eventually be run in the JVM and cannot stand-alone.

Java Code: System.out.println("hello") (To be compiled)  Compiled Java bytecode: Print "hello" (To be run in JVM)  JVM: (... some translation, maybe to architecture code - I forget exactly ...) system_print_code "hello" (JVM translation to CPU specific) 

Versus the C++ (which can be run in stand-alone mode):

C++ Code: cout<< "hello";  Architecture Code: some_assembly_routine "hello"  Binary output: system_print_code "hello" 

A real example

If you're curious about how this may actually look in a real-life example, I have included one below.

C++ Source I placed this in a file called hello.cpp

#include <iostream>  int main() {   using namespace std;   cout << "Hello world!" << endl;   return 0; } 

Assembly (Generated from C++ source) Generated via g++ -S hello.cpp

    .file   "test.c"     .section    .rodata     .type   _ZStL19piecewise_construct, @object     .size   _ZStL19piecewise_construct, 1 _ZStL19piecewise_construct:     .zero   1     .local  _ZStL8__ioinit     .comm   _ZStL8__ioinit,1,1 .LC0:     .string "Hello world!"     .text     .globl  main     .type   main, @function main: .LFB1493:     .cfi_startproc     pushq   %rbp     .cfi_def_cfa_offset 16     .cfi_offset 6, -16     movq    %rsp, %rbp     .cfi_def_cfa_register 6     leaq    .LC0(%rip), %rsi     leaq    _ZSt4cout(%rip), %rdi     call    _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc@PLT     movq    %rax, %rdx     movq    _ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_@GOTPCREL(%rip), %rax     movq    %rax, %rsi     movq    %rdx, %rdi     call    _ZNSolsEPFRSoS_E@PLT     movl    $0, %eax     popq    %rbp     .cfi_def_cfa 7, 8     ret     .cfi_endproc .LFE1493:     .size   main, .-main     .type   _Z41__static_initialization_and_destruction_0ii, @function _Z41__static_initialization_and_destruction_0ii: .LFB1982:     .cfi_startproc     pushq   %rbp     .cfi_def_cfa_offset 16     .cfi_offset 6, -16     movq    %rsp, %rbp     .cfi_def_cfa_register 6     subq    $16, %rsp     movl    %edi, -4(%rbp)     movl    %esi, -8(%rbp)     cmpl    $1, -4(%rbp)     jne .L5     cmpl    $65535, -8(%rbp)     jne .L5     leaq    _ZStL8__ioinit(%rip), %rdi     call    _ZNSt8ios_base4InitC1Ev@PLT     leaq    __dso_handle(%rip), %rdx     leaq    _ZStL8__ioinit(%rip), %rsi     movq    _ZNSt8ios_base4InitD1Ev@GOTPCREL(%rip), %rax     movq    %rax, %rdi     call    __cxa_atexit@PLT .L5:     nop     leave     .cfi_def_cfa 7, 8     ret     .cfi_endproc .LFE1982:     .size   _Z41__static_initialization_and_destruction_0ii, .-_Z41__static_initialization_and_destruction_0ii     .type   _GLOBAL__sub_I_main, @function _GLOBAL__sub_I_main: .LFB1983:     .cfi_startproc     pushq   %rbp     .cfi_def_cfa_offset 16     .cfi_offset 6, -16     movq    %rsp, %rbp     .cfi_def_cfa_register 6     movl    $65535, %esi     movl    $1, %edi     call    _Z41__static_initialization_and_destruction_0ii     popq    %rbp     .cfi_def_cfa 7, 8     ret     .cfi_endproc .LFE1983:     .size   _GLOBAL__sub_I_main, .-_GLOBAL__sub_I_main     .section    .init_array,"aw"     .align 8     .quad   _GLOBAL__sub_I_main     .hidden __dso_handle     .ident  "GCC: (GNU) 7.2.1 20171128"     .section    .note.GNU-stack,"",@progbits 

Binary output (Generated from assembly) This is the unlinked form (i.e. not yet fully populated with symbol locations) of the binary output generated via g++ -c in hexadecimal form. I generated the hexadecimal representation using xxd.

00000000: 7f45 4c46 0201 0100 0000 0000 0000 0000  .ELF............ 00000010: 0100 3e00 0100 0000 0000 0000 0000 0000  ..>............. 00000020: 0000 0000 0000 0000 0807 0000 0000 0000  ................ 00000030: 0000 0000 4000 0000 0000 4000 0f00 0e00  ....@.....@..... 00000040: 5548 89e5 488d 3500 0000 0048 8d3d 0000  UH..H.5....H.=.. 00000050: 0000 e800 0000 0048 89c2 488b 0500 0000  .......H..H..... 00000060: 0048 89c6 4889 d7e8 0000 0000 b800 0000  .H..H........... 00000070: 005d c355 4889 e548 83ec 1089 7dfc 8975  .].UH..H....}..u 00000080: f883 7dfc 0175 3281 7df8 ffff 0000 7529  ..}..u2.}.....u) 00000090: 488d 3d00 0000 00e8 0000 0000 488d 1500  H.=.........H... 000000a0: 0000 0048 8d35 0000 0000 488b 0500 0000  ...H.5....H..... 000000b0: 0048 89c7 e800 0000 0090 c9c3 5548 89e5  .H..........UH.. 000000c0: beff ff00 00bf 0100 0000 e8a4 ffff ff5d  ...............] 000000d0: c300 4865 6c6c 6f20 776f 726c 6421 0000  ..Hello world!.. 000000e0: 0000 0000 0000 0000 0047 4343 3a20 2847  .........GCC: (G 000000f0: 4e55 2920 372e 322e 3120 3230 3137 3131  NU) 7.2.1 201711 00000100: 3238 0000 0000 0000 1400 0000 0000 0000  28.............. 00000110: 017a 5200 0178 1001 1b0c 0708 9001 0000  .zR..x.......... 00000120: 1c00 0000 1c00 0000 0000 0000 3300 0000  ............3... 00000130: 0041 0e10 8602 430d 066e 0c07 0800 0000  .A....C..n...... 00000140: 1c00 0000 3c00 0000 0000 0000 4900 0000  ....<.......I... 00000150: 0041 0e10 8602 430d 0602 440c 0708 0000  .A....C...D..... 00000160: 1c00 0000 5c00 0000 0000 0000 1500 0000  ....\........... 00000170: 0041 0e10 8602 430d 0650 0c07 0800 0000  .A....C..P...... 00000180: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000190: 0000 0000 0000 0000 0100 0000 0400 f1ff  ................ 000001a0: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 000001b0: 0000 0000 0300 0100 0000 0000 0000 0000  ................ 000001c0: 0000 0000 0000 0000 0000 0000 0300 0300  ................ 000001d0: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 000001e0: 0000 0000 0300 0400 0000 0000 0000 0000  ................ 000001f0: 0000 0000 0000 0000 0000 0000 0300 0500  ................ 00000200: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000210: 0800 0000 0100 0500 0000 0000 0000 0000  ................ 00000220: 0100 0000 0000 0000 2300 0000 0100 0400  ........#....... 00000230: 0000 0000 0000 0000 0100 0000 0000 0000  ................ 00000240: 3200 0000 0200 0100 3300 0000 0000 0000  2.......3....... 00000250: 4900 0000 0000 0000 6200 0000 0200 0100  I.......b....... 00000260: 7c00 0000 0000 0000 1500 0000 0000 0000  |............... 00000270: 0000 0000 0300 0600 0000 0000 0000 0000  ................ 00000280: 0000 0000 0000 0000 0000 0000 0300 0900  ................ 00000290: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 000002a0: 0000 0000 0300 0a00 0000 0000 0000 0000  ................ 000002b0: 0000 0000 0000 0000 0000 0000 0300 0800  ................ 000002c0: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 000002d0: 7100 0000 1200 0100 0000 0000 0000 0000  q............... 000002e0: 3300 0000 0000 0000 7600 0000 1000 0000  3.......v....... 000002f0: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000300: 8000 0000 1000 0000 0000 0000 0000 0000  ................ 00000310: 0000 0000 0000 0000 9600 0000 1000 0000  ................ 00000320: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000330: ce00 0000 1000 0000 0000 0000 0000 0000  ................ 00000340: 0000 0000 0000 0000 0901 0000 1000 0000  ................ 00000350: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000360: 1a01 0000 1000 0000 0000 0000 0000 0000  ................ 00000370: 0000 0000 0000 0000 3201 0000 1002 0000  ........2....... 00000380: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000390: 3f01 0000 1000 0000 0000 0000 0000 0000  ?............... 000003a0: 0000 0000 0000 0000 5701 0000 1000 0000  ........W....... 000003b0: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 000003c0: 0074 6573 742e 6300 5f5a 5374 4c31 3970  .test.c._ZStL19p 000003d0: 6965 6365 7769 7365 5f63 6f6e 7374 7275  iecewise_constru 000003e0: 6374 005f 5a53 744c 385f 5f69 6f69 6e69  ct._ZStL8__ioini 000003f0: 7400 5f5a 3431 5f5f 7374 6174 6963 5f69  t._Z41__static_i 00000400: 6e69 7469 616c 697a 6174 696f 6e5f 616e  nitialization_an 00000410: 645f 6465 7374 7275 6374 696f 6e5f 3069  d_destruction_0i 00000420: 6900 5f47 4c4f 4241 4c5f 5f73 7562 5f49  i._GLOBAL__sub_I 00000430: 5f6d 6169 6e00 5f5a 5374 3463 6f75 7400  _main._ZSt4cout. 00000440: 5f47 4c4f 4241 4c5f 4f46 4653 4554 5f54  _GLOBAL_OFFSET_T 00000450: 4142 4c45 5f00 5f5a 5374 6c73 4953 7431  ABLE_._ZStlsISt1 00000460: 3163 6861 725f 7472 6169 7473 4963 4545  1char_traitsIcEE 00000470: 5253 7431 3362 6173 6963 5f6f 7374 7265  RSt13basic_ostre 00000480: 616d 4963 545f 4553 355f 504b 6300 5f5a  amIcT_ES5_PKc._Z 00000490: 5374 3465 6e64 6c49 6353 7431 3163 6861  St4endlIcSt11cha 000004a0: 725f 7472 6169 7473 4963 4545 5253 7431  r_traitsIcEERSt1 000004b0: 3362 6173 6963 5f6f 7374 7265 616d 4954  3basic_ostreamIT 000004c0: 5f54 305f 4553 365f 005f 5a4e 536f 6c73  _T0_ES6_._ZNSols 000004d0: 4550 4652 536f 535f 4500 5f5a 4e53 7438  EPFRSoS_E._ZNSt8 000004e0: 696f 735f 6261 7365 3449 6e69 7443 3145  ios_base4InitC1E 000004f0: 7600 5f5f 6473 6f5f 6861 6e64 6c65 005f  v.__dso_handle._ 00000500: 5a4e 5374 3869 6f73 5f62 6173 6534 496e  ZNSt8ios_base4In 00000510: 6974 4431 4576 005f 5f63 7861 5f61 7465  itD1Ev.__cxa_ate 00000520: 7869 7400 0000 0000 0700 0000 0000 0000  xit............. 00000530: 0200 0000 0500 0000 fdff ffff ffff ffff  ................ 00000540: 0e00 0000 0000 0000 0200 0000 0f00 0000  ................ 00000550: fcff ffff ffff ffff 1300 0000 0000 0000  ................ 00000560: 0400 0000 1100 0000 fcff ffff ffff ffff  ................ 00000570: 1d00 0000 0000 0000 2a00 0000 1200 0000  ........*....... 00000580: fcff ffff ffff ffff 2800 0000 0000 0000  ........(....... 00000590: 0400 0000 1300 0000 fcff ffff ffff ffff  ................ 000005a0: 5300 0000 0000 0000 0200 0000 0400 0000  S............... 000005b0: fcff ffff ffff ffff 5800 0000 0000 0000  ........X....... 000005c0: 0400 0000 1400 0000 fcff ffff ffff ffff  ................ 000005d0: 5f00 0000 0000 0000 0200 0000 1500 0000  _............... 000005e0: fcff ffff ffff ffff 6600 0000 0000 0000  ........f....... 000005f0: 0200 0000 0400 0000 fcff ffff ffff ffff  ................ 00000600: 6d00 0000 0000 0000 2a00 0000 1600 0000  m.......*....... 00000610: fcff ffff ffff ffff 7500 0000 0000 0000  ........u....... 00000620: 0400 0000 1700 0000 fcff ffff ffff ffff  ................ 00000630: 0000 0000 0000 0000 0100 0000 0200 0000  ................ 00000640: 7c00 0000 0000 0000 2000 0000 0000 0000  |....... ....... 00000650: 0200 0000 0200 0000 0000 0000 0000 0000  ................ 00000660: 4000 0000 0000 0000 0200 0000 0200 0000  @............... 00000670: 3300 0000 0000 0000 6000 0000 0000 0000  3.......`....... 00000680: 0200 0000 0200 0000 7c00 0000 0000 0000  ........|....... 00000690: 002e 7379 6d74 6162 002e 7374 7274 6162  ..symtab..strtab 000006a0: 002e 7368 7374 7274 6162 002e 7265 6c61  ..shstrtab..rela 000006b0: 2e74 6578 7400 2e64 6174 6100 2e62 7373  .text..data..bss 000006c0: 002e 726f 6461 7461 002e 7265 6c61 2e69  ..rodata..rela.i 000006d0: 6e69 745f 6172 7261 7900 2e63 6f6d 6d65  nit_array..comme 000006e0: 6e74 002e 6e6f 7465 2e47 4e55 2d73 7461  nt..note.GNU-sta 000006f0: 636b 002e 7265 6c61 2e65 685f 6672 616d  ck..rela.eh_fram 00000700: 6500 0000 0000 0000 0000 0000 0000 0000  e............... 00000710: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000720: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000730: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000740: 0000 0000 0000 0000 2000 0000 0100 0000  ........ ....... 00000750: 0600 0000 0000 0000 0000 0000 0000 0000  ................ 00000760: 4000 0000 0000 0000 9100 0000 0000 0000  @............... 00000770: 0000 0000 0000 0000 0100 0000 0000 0000  ................ 00000780: 0000 0000 0000 0000 1b00 0000 0400 0000  ................ 00000790: 4000 0000 0000 0000 0000 0000 0000 0000  @............... 000007a0: 2805 0000 0000 0000 0801 0000 0000 0000  (............... 000007b0: 0c00 0000 0100 0000 0800 0000 0000 0000  ................ 000007c0: 1800 0000 0000 0000 2600 0000 0100 0000  ........&....... 000007d0: 0300 0000 0000 0000 0000 0000 0000 0000  ................ 000007e0: d100 0000 0000 0000 0000 0000 0000 0000  ................ 000007f0: 0000 0000 0000 0000 0100 0000 0000 0000  ................ 00000800: 0000 0000 0000 0000 2c00 0000 0800 0000  ........,....... 00000810: 0300 0000 0000 0000 0000 0000 0000 0000  ................ 00000820: d100 0000 0000 0000 0100 0000 0000 0000  ................ 00000830: 0000 0000 0000 0000 0100 0000 0000 0000  ................ 00000840: 0000 0000 0000 0000 3100 0000 0100 0000  ........1....... 00000850: 0200 0000 0000 0000 0000 0000 0000 0000  ................ 00000860: d100 0000 0000 0000 0e00 0000 0000 0000  ................ 00000870: 0000 0000 0000 0000 0100 0000 0000 0000  ................ 00000880: 0000 0000 0000 0000 3e00 0000 0e00 0000  ........>....... 00000890: 0300 0000 0000 0000 0000 0000 0000 0000  ................ 000008a0: e000 0000 0000 0000 0800 0000 0000 0000  ................ 000008b0: 0000 0000 0000 0000 0800 0000 0000 0000  ................ 000008c0: 0800 0000 0000 0000 3900 0000 0400 0000  ........9....... 000008d0: 4000 0000 0000 0000 0000 0000 0000 0000  @............... 000008e0: 3006 0000 0000 0000 1800 0000 0000 0000  0............... 000008f0: 0c00 0000 0600 0000 0800 0000 0000 0000  ................ 00000900: 1800 0000 0000 0000 4a00 0000 0100 0000  ........J....... 00000910: 3000 0000 0000 0000 0000 0000 0000 0000  0............... 00000920: e800 0000 0000 0000 1b00 0000 0000 0000  ................ 00000930: 0000 0000 0000 0000 0100 0000 0000 0000  ................ 00000940: 0100 0000 0000 0000 5300 0000 0100 0000  ........S....... 00000950: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000960: 0301 0000 0000 0000 0000 0000 0000 0000  ................ 00000970: 0000 0000 0000 0000 0100 0000 0000 0000  ................ 00000980: 0000 0000 0000 0000 6800 0000 0100 0000  ........h....... 00000990: 0200 0000 0000 0000 0000 0000 0000 0000  ................ 000009a0: 0801 0000 0000 0000 7800 0000 0000 0000  ........x....... 000009b0: 0000 0000 0000 0000 0800 0000 0000 0000  ................ 000009c0: 0000 0000 0000 0000 6300 0000 0400 0000  ........c....... 000009d0: 4000 0000 0000 0000 0000 0000 0000 0000  @............... 000009e0: 4806 0000 0000 0000 4800 0000 0000 0000  H.......H....... 000009f0: 0c00 0000 0a00 0000 0800 0000 0000 0000  ................ 00000a00: 1800 0000 0000 0000 0100 0000 0200 0000  ................ 00000a10: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000a20: 8001 0000 0000 0000 4002 0000 0000 0000  ........@....... 00000a30: 0d00 0000 0e00 0000 0800 0000 0000 0000  ................ 00000a40: 1800 0000 0000 0000 0900 0000 0300 0000  ................ 00000a50: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000a60: c003 0000 0000 0000 6401 0000 0000 0000  ........d....... 00000a70: 0000 0000 0000 0000 0100 0000 0000 0000  ................ 00000a80: 0000 0000 0000 0000 1100 0000 0300 0000  ................ 00000a90: 0000 0000 0000 0000 0000 0000 0000 0000  ................ 00000aa0: 9006 0000 0000 0000 7200 0000 0000 0000  ........r....... 00000ab0: 0000 0000 0000 0000 0100 0000 0000 0000  ................ 00000ac0: 0000 0000 0000 0000                      ........ 

These instructions correspond to an x86_64 machine. If you're interested in following along and matching the op codes, you can look at this reference or download the Intel manual for completeness. Likewise, it is an ELF file so you can observe that we see things we expect (i.e. starting magic number of 0x7f, etc.).

In any case, once linked against the system (i.e. run g++ test.cpp or g++ test.s or g++ test.o), this executable runs directly on top of your OS. There are no additional translation layers between this and the OS. Even so, the OS still does OS things like abstracting hardware interfaces, manage system resources, etc.

Tying this back to the original question, the output binary will look very different on a windows machine (for the same C++ code). At the very least, on a windows machine you would expect to see the file in the Portable Executable (PE) format which is distinctly not ELF.

This is unlike the following Java example which requires a JVM to run:

Java Source File This is placed in a file called Test.java

package mytest;  public class Test {   public static void main(String[] args) {     System.out.println("Hello world!");   } } 

Java Byte Code (Generated from Java Source) This is generated by running javac -d . Test.java and running the output file (i.e. mytest/Test.class) through xxd

00000000: cafe babe 0000 0034 001d 0a00 0600 0f09  .......4........ 00000010: 0010 0011 0800 120a 0013 0014 0700 1507  ................ 00000020: 0016 0100 063c 696e 6974 3e01 0003 2829  .....<init>...() 00000030: 5601 0004 436f 6465 0100 0f4c 696e 654e  V...Code...LineN 00000040: 756d 6265 7254 6162 6c65 0100 046d 6169  umberTable...mai 00000050: 6e01 0016 285b 4c6a 6176 612f 6c61 6e67  n...([Ljava/lang 00000060: 2f53 7472 696e 673b 2956 0100 0a53 6f75  /String;)V...Sou 00000070: 7263 6546 696c 6501 0009 5465 7374 2e6a  rceFile...Test.j 00000080: 6176 610c 0007 0008 0700 170c 0018 0019  ava............. 00000090: 0100 0c48 656c 6c6f 2077 6f72 6c64 2107  ...Hello world!. 000000a0: 001a 0c00 1b00 1c01 000b 6d79 7465 7374  ..........mytest 000000b0: 2f54 6573 7401 0010 6a61 7661 2f6c 616e  /Test...java/lan 000000c0: 672f 4f62 6a65 6374 0100 106a 6176 612f  g/Object...java/ 000000d0: 6c61 6e67 2f53 7973 7465 6d01 0003 6f75  lang/System...ou 000000e0: 7401 0015 4c6a 6176 612f 696f 2f50 7269  t...Ljava/io/Pri 000000f0: 6e74 5374 7265 616d 3b01 0013 6a61 7661  ntStream;...java 00000100: 2f69 6f2f 5072 696e 7453 7472 6561 6d01  /io/PrintStream. 00000110: 0007 7072 696e 746c 6e01 0015 284c 6a61  ..println...(Lja 00000120: 7661 2f6c 616e 672f 5374 7269 6e67 3b29  va/lang/String;) 00000130: 5600 2100 0500 0600 0000 0000 0200 0100  V.!............. 00000140: 0700 0800 0100 0900 0000 1d00 0100 0100  ................ 00000150: 0000 052a b700 01b1 0000 0001 000a 0000  ...*............ 00000160: 0006 0001 0000 0003 0009 000b 000c 0001  ................ 00000170: 0009 0000 0025 0002 0001 0000 0009 b200  .....%.......... 00000180: 0212 03b6 0004 b100 0000 0100 0a00 0000  ................ 00000190: 0a00 0200 0000 0500 0800 0600 0100 0d00  ................ 000001a0: 0000 0200 0e                             ..... 

As one would expect, the byte code output starts with 0xCAFEBABE.

The critical distinction here, however, is that this code cannot be run directly. It is still a binary output, but it's not intended to be executed directly by the operating system. If you tried to run this without a JVM on your system, you would just get an error. However, this code can be run on any operating system that contains a compatible JVM. The set of compatible JVM's depends on how you've set your source and target. By default, it's equivalent to the Java version you're using to compile. In this case, I used Java 8.

The way this works is that your JVM is compiled for each system specifically (similarly to the C++ example above) and translates its binary Java byte code into something your system can now execute.

At the end of the day, there is no free lunch-- as DanielKO mentioned in the comments, the JVM is still a "platform" but it's one-level higher than the OS so it can seem a bit more portable. Eventually, somewhere along the way, the code must translate to instructions valid for your specific operating system family and CPU architecture. However, in the case of Java and the JVM, you only have to compile a single application (i.e. the JVM itself) for all system flavors. At that point, everything written on top of the JVM has system support "for free" so to speak (as long as your application is entirely written in Java and isn't using native interfaces, etc.).

As I mentioned before, there are many caveats to this information :) This was a pretty straightforward example intended to illustrate what you might actually observe. That said, we didn't get into calling native code, using custom JVM agents, or anything else which may affect this answer slightly. In general, however, these more often fall into the category of "special cases" and you wouldn't often be using these things unless you understood why and (hopefully) their implications to portability.

Answer 2

C++ is not platform dependent - in fact there is a standard that all vendors try to implement. What you mean is that the EXECUTABLE that is produced is platform dependent. That is because each OS has a different definition and requirements of what constitutes a valid executable file. Also, each OS has a different set of APIs used for implementing core services that need to be linked against by the C++ linker and compiler. But this has nothing to do with C++ as a language.

Answer 3

What makes a language, such as C++, "platform independent" is that it doesn't rely upon language constructs that are heavily favored by a given CPU architecture. Assembly language, for example and in contrast, is quite specific to a CPU architecture and instruction set. The front-end of a C++ compiler (parsing and semantic analysis) can be the same or basically the same for any computing platform it's targeted for. However, there still needs to be a platform or CPU specific code generator (e.g., for x86, ARM, etc).

An EXE is a binary file specifically compiled and code-generated for DOS/Windows platform. It's structure is known by the DOS/Windows system and it contains information for how to locate the executable in memory as well as all of the instruction codes specific to CPU/platform for it to run. As indicated by Oleksandr, its specific format can be found, for example, on Wikipedia.

Answer 4

Actually C++ is not a platform dependent, but the output it produces is in .exe or other format which is depend on the platform you are using. so simply C++'s code is independent of platform, just the output comes after compilation is dependent.