CODEWITHSUNDEEP
c++macrosbyte
Basav Nagar
Basav Nagar

Reputation: 27

Macro gives problems in gcc

#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;
}

When I try to compile, I get this error,related to increment operand 

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

Anyone please shed light on this???

Upvotes: 1

Views: 188

Answers (2)

sandymatt
sandymatt

Reputation: 5612

Macros will essentially perform a text replacement that happens via the pre-processor.

The macro will turn your code into something like 1++ and 5++. These are integer literals, which means the compiler marks them as 'pure' rvalues (prvalues). prvalues are not the same as l-values

Upvotes: 3

Jonathan Leffler
Jonathan Leffler

Reputation: 754160

Given that you apply a ++ operator to the pos argument, you cannot pass a constant like 1 or 5 as the third argument to the macro. Any compiler that let you do that would be erroneous.

Upvotes: 2

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