宏給出了GCC

Question

#include<vector> 
#include<stdint.h> 
#define RAM_M_V_INSERT_T32(vec,Long,pos) \ 
vec.at(pos)=(((tU8)((Long) >> 24)) & 0xFF); \ 
pos++;\ 
vec.at(pos)=(((tU8)((Long) >> 16)) & 0xFF); \ 
pos++;\ 
vec.at(pos)=(((tU8)((Long) >> 8)) & 0xFF); \ 
pos++;\ 
vec.at(pos)=(((tU8)((Long))) & 0xFF); 

int main() 
{ 
std::vector<char> c8vBuf; 
c8vBuf.at(0)=(char)SYSTEM_U32_SHUTDOWN_CPU_WATCHDOG; 
RAM_M_V_INSERT_T32(c8vBuf, (_u32WdtCount - 1),1); 
RAM_M_V_INSERT_T32(c8vBuf, _u32WdtCount,5); 
return 0; 
} 

當我嘗試編譯的問題，我得到這個錯誤，有關遞增操作數

cstr.cpp:19:3: error: lvalue required as increment operand 
cstr.cpp:19:3: error: lvalue required as increment operand 
cstr.cpp:19:3: error: lvalue required as increment operand 
cstr.cpp:20:3: error: lvalue required as increment operand 
cstr.cpp:20:3: error: lvalue required as increment operand 
cstr.cpp:20:3: error: lvalue required as increment operand 

請人闡明這光???

Answer 1

宏將基本上執行通過預處理器發生的文本替換。

該宏會將您的代碼變成類似1++和5++的東西。這些是整數文字，這意味着編譯器將它們標記爲「純」rvalues（prvalues）。 prvalues與l值不同

Answer 2

鑑於您將++運算符應用於參數pos，您不能將類似1或5的常量作爲第三個參數傳遞給宏。任何讓你這樣做的編譯器都是錯誤的。