Passing Multiple Parameters In Dev C++
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This section describes the standard processes and conventions that one function (the caller) uses to make calls into another function (the callee) in x64 code.
Calling convention defaults
Php Passing Parameters
Now here's one that DOES work, but does not parse any arguments. However, it does pass an ostream parameter to a function and the function writes either to the screen and to a file. I want to pass a stream to function and have the function write to it. Everything that follows /C (or /K) is a new command line, so it must be the last parameter specified when calling cmd.exe. This is stated in the documentation for /C (and /K ): If /C or /K is specified, then the remainder of the command line after the switch is processed as a command line. Apr 12, 2013 C Tutorial 13 - Passing by Value vs Passing by Reference - Duration: 15:01. Programminghelporg 111,470 views. How to Pass vector as a function parameter in C When we pass a vector to a function, a copy of this vector is created. For example, we can see below program, changes made inside the function are not reflected outside because function has a copy.
The x64 Application Binary Interface (ABI) uses a four-register fast-call calling convention by default. Space is allocated on the call stack as a shadow store for callees to save those registers. There's a strict one-to-one correspondence between the arguments to a function call and the registers used for those arguments. Any argument that doesn't fit in 8 bytes, or isn't 1, 2, 4, or 8 bytes, must be passed by reference. A single argument is never spread across multiple registers. The x87 register stack is unused, and may be used by the callee, but must be considered volatile across function calls. All floating point operations are done using the 16 XMM registers. Integer arguments are passed in registers RCX, RDX, R8, and R9. Floating point arguments are passed in XMM0L, XMM1L, XMM2L, and XMM3L. 16-byte arguments are passed by reference. Parameter passing is described in detail in Parameter Passing. In addition to these registers, RAX, R10, R11, XMM4, and XMM5 are considered volatile. All other registers are non-volatile. Register usage is documented in detail in Register Usage and Caller/Callee Saved Registers.
For prototyped functions, all arguments are converted to the expected callee types before passing. The caller is responsible for allocating space for parameters to the callee, and must always allocate sufficient space to store four register parameters, even if the callee doesn't take that many parameters. This convention simplifies support for unprototyped C-language functions and vararg C/C++ functions. For vararg or unprototyped functions, any floating point values must be duplicated in the corresponding general-purpose register. Any parameters beyond the first four must be stored on the stack after the shadow store prior to the call. Vararg function details can be found in Varargs. Unprototyped function information is detailed in Unprototyped Functions.
Alignment
Most structures are aligned to their natural alignment. The primary exceptions are the stack pointer and malloc or alloca memory, which are aligned to 16 bytes in order to aid performance. Alignment above 16 bytes must be done manually, but since 16 bytes is a common alignment size for XMM operations, this value should work for most code. For more information about structure layout and alignment, see Types and Storage. For information about the stack layout, see x64 stack usage.
Unwindability
Leaf functions are functions that don't change any non-volatile registers. A non-leaf function may change non-volatile RSP, for example, by calling a function or allocating additional stack space for local variables. In order to recover non-volatile registers when an exception is handled, non-leaf functions must be annotated with static data that describes how to properly unwind the function at an arbitrary instruction. This data is stored as pdata, or procedure data, which in turn refers to xdata, the exception handling data. The xdata contains the unwinding information, and can point to additional pdata or an exception handler function. Prologs and epilogs are highly restricted so that they can be properly described in xdata. The stack pointer must be aligned to 16 bytes in any region of code that isn't part of an epilog or prolog, except within leaf functions. Leaf functions can be unwound simply by simulating a return, so pdata and xdata are not required. For details about the proper structure of function prologs and epilogs, see x64 prolog and epilog. For more information about exception handling, and the exception handling and unwinding of pdata and xdata, see x64 exception handling.
Parameter passing
The first four integer arguments are passed in registers. Integer values are passed in left-to-right order in RCX, RDX, R8, and R9, respectively. Arguments five and higher are passed on the stack. All arguments are right-justified in registers, so the callee can ignore the upper bits of the register and access only the portion of the register necessary.
Any floating-point and double-precision arguments in the first four parameters are passed in XMM0 - XMM3, depending on position. The integer registers RCX, RDX, R8, and R9 that would normally be used for those positions are ignored, except in the case of varargs arguments. For details, see Varargs. Similarly, the XMM0 - XMM3 registers are ignored when the corresponding argument is an integer or pointer type.
__m128 types, arrays, and strings are never passed by immediate value. Instead, a pointer is passed to memory allocated by the caller. Structs and unions of size 8, 16, 32, or 64 bits, and __m64 types, are passed as if they were integers of the same size. Structs or unions of other sizes are passed as a pointer to memory allocated by the caller. For these aggregate types passed as a pointer, including __m128, the caller-allocated temporary memory must be 16-byte aligned.
Intrinsic functions that don't allocate stack space, and don't call other functions, sometimes use other volatile registers to pass additional register arguments. This optimization is made possible by the tight binding between the compiler and the intrinsic function implementation.
The callee is responsible for dumping the register parameters into their shadow space if needed.
The following table summarizes how parameters are passed:
| Parameter type | How passed |
|---|---|
| Floating point | First 4 parameters - XMM0 through XMM3. Others passed on stack. |
| Integer | First 4 parameters - RCX, RDX, R8, R9. Others passed on stack. |
| Aggregates (8, 16, 32, or 64 bits) and __m64 | First 4 parameters - RCX, RDX, R8, R9. Others passed on stack. |
| Aggregates (other) | By pointer. First 4 parameters passed as pointers in RCX, RDX, R8, and R9 |
| __m128 | By pointer. First 4 parameters passed as pointers in RCX, RDX, R8, and R9 |
Example of argument passing 1 - all integers
Example of argument passing 2 - all floats
Example of argument passing 3 - mixed ints and floats
Example of argument passing 4 -__m64, __m128, and aggregates
Varargs
If parameters are passed via varargs (for example, ellipsis arguments), then the normal register parameter passing convention applies, including spilling the fifth and subsequent arguments to the stack. It's the callee's responsibility to dump arguments that have their address taken. For floating-point values only, both the integer register and the floating-point register must contain the value, in case the callee expects the value in the integer registers.
Unprototyped functions
For functions not fully prototyped, the caller passes integer values as integers and floating-point values as double precision. For floating-point values only, both the integer register and the floating-point register contain the float value in case the callee expects the value in the integer registers.
Return values
A scalar return value that can fit into 64 bits is returned through RAX; this includes __m64 types. Non-scalar types including floats, doubles, and vector types such as __m128, __m128i, __m128d are returned in XMM0. The state of unused bits in the value returned in RAX or XMM0 is undefined.
User-defined types can be returned by value from global functions and static member functions. To return a user-defined type by value in RAX, it must have a length of 1, 2, 4, 8, 16, 32, or 64 bits. It must also have no user-defined constructor, destructor, or copy assignment operator; no private or protected non-static data members; no non-static data members of reference type; no base classes; no virtual functions; and no data members that do not also meet these requirements. (This is essentially the definition of a C++03 POD type. Because the definition has changed in the C++11 standard, we don't recommend using std::is_pod for this test.) Otherwise, the caller assumes the responsibility of allocating memory and passing a pointer for the return value as the first argument. Subsequent arguments are then shifted one argument to the right. The same pointer must be returned by the callee in RAX.
These examples show how parameters and return values are passed for functions with the specified declarations:
Example of return value 1 - 64-bit result
Example of return value 2 - 128-bit result
Example of return value 3 - user type result by pointer
Example of return value 4 - user type result by value
Caller/Callee saved registers
The registers RAX, RCX, RDX, R8, R9, R10, R11, XMM0-5, and the upper portions of YMM0-15 and ZMM0-15 are considered volatile and must be considered destroyed on function calls (unless otherwise safety-provable by analysis such as whole program optimization). On AVX512VL, the ZMM, YMM, and XMM registers 16-31 are volatile.
The registers RBX, RBP, RDI, RSI, RSP, R12, R13, R14, R15, and XMM6-15 are considered nonvolatile and must be saved and restored by a function that uses them.
Function pointers
Function pointers are simply pointers to the label of the respective function. There are no table of contents (TOC) requirements for function pointers.
Floating-point support for older code
The MMX and floating-point stack registers (MM0-MM7/ST0-ST7) are preserved across context switches. There is no explicit calling convention for these registers. The use of these registers is strictly prohibited in kernel mode code.
FpCsr
The register state also includes the x87 FPU control word. The calling convention dictates this register to be nonvolatile.
The x87 FPU control word register is set to the following standard values at the start of program execution:
| Register[bits] | Setting |
|---|---|
| FPCSR[0:6] | Exception masks all 1's (all exceptions masked) |
| FPCSR[7] | Reserved - 0 |
| FPCSR[8:9] | Precision Control - 10B (double precision) |
| FPCSR[10:11] | Rounding control - 0 (round to nearest) |
| FPCSR[12] | Infinity control - 0 (not used) |
A callee that modifies any of the fields within FPCSR must restore them before returning to its caller. Furthermore, a caller that has modified any of these fields must restore them to their standard values before invoking a callee unless by agreement the callee expects the modified values.
There are two exceptions to the rules about the non-volatility of the control flags:
In functions where the documented purpose of the given function is to modify the nonvolatile FpCsr flags.
When it's provably correct that the violation of these rules results in a program that behaves the same as a program where these rules aren't violated, for example, through whole-program analysis.
MxCsr
Auto tune evo download tutorials. The register state also includes MxCsr. The calling convention divides this register into a volatile portion and a nonvolatile portion. The volatile portion consists of the six status flags, in MXCSR[0:5], while the rest of the register, MXCSR[6:15], is considered nonvolatile.
The nonvolatile portion is set to the following standard values at the start of program execution:
| Register[bits] | Setting |
|---|---|
| MXCSR[6] | Denormals are zeros - 0 |
| MXCSR[7:12] | Exception masks all 1's (all exceptions masked) |
| MXCSR[13:14] | Rounding control - 0 (round to nearest) |
| MXCSR[15] | Flush to zero for masked underflow - 0 (off) |
A callee that modifies any of the nonvolatile fields within MXCSR must restore them before returning to its caller. Furthermore, a caller that has modified any of these fields must restore them to their standard values before invoking a callee unless by agreement the callee expects the modified values.
C++ Reference Function Parameter
There are two exceptions to the rules about the non-volatility of the control flags:
In functions where the documented purpose of the given function is to modify the nonvolatile MxCsr flags.
When it's provably correct that the violation of these rules results in a program that behaves the same as a program where these rules aren't violated, for example, through whole-program analysis.
No assumptions can be made about the state of the volatile portion of MXCSR across a function boundary, unless specifically described in a function's documentation.
setjmp/longjmp
When you include setjmpex.h or setjmp.h, all calls to setjmp or longjmp result in an unwind that invokes destructors and __finally calls. This differs from x86, where including setjmp.h results in __finally clauses and destructors not being invoked.
A call to setjmp preserves the current stack pointer, non-volatile registers, and MxCsr registers. Calls to longjmp return to the most recent setjmp call site and resets the stack pointer, non-volatile registers, and MxCsr registers, back to the state as preserved by the most recent setjmp call.
See also
I'm trying to createa function that takes command line arguments, parses them, and returns a stream to be used for output. If a filename is specified, the program will write to that file. If no filename is specified, the default output will be to cout.
I haven't gotten to the parsing yet. Simply passing an ostream parameter and trying to assign it to equal cout is giving me preoblems already. The error is one of those really long errors, so I won't post it unless someone wants it. I've tried making line 15 either an ostream or an ofstream. Neither works.
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The easiest thing in this case is to just use a smart pointer, as so:
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mike_2000_172,669
You cannot do what you are trying to do because objects in C++ are not references, they are objects. When you create the outs object in main(), you create an object, not a reference to another object, so you cannot 're-seat' it by making it refer to something else (in particular, std::cout). One simple way to achieve what you are trying to achieve is to do the following:
That's one simple way to do things, it is not super-robust, of course, you should implement the global-out as a proper singleton implementation, but you get the idea. And, technically, outputs that would occur after main has finished would be unsafe, but that's always the case anyways.