[英]How to address a float to write 4 individual bytes to it in C?
我有一个函数,期望32位浮点数,但是在某种模式下,它期望浮点数实际上只是打包在一起的4x UINT8s。
我编写的代码有效,但是我得到了编译器警告“非法指针”警告,并且我想知道最“正确”的方法是什么? 代码的可读性也非常重要,尽管可能有更少的代码编写方式,但我认为我写的内容很容易阅读。
UINT8 time[6];
FLOAT FSTtime = 0; //32bit float
UINT8 * FSTtimePointer;
//Get the current time as 6 bytes {secs,mins,hours,day,month,year}
returnSize = appP->DB_get_param_value(12, 0, 8, &time);
if (returnSize < 6) return;
(UINT8*)FSTtimePointer = &FSTtime; //Line 876
//Pack 4 bytes of time data into a "float"
FSTtimePointer [0] = time[3]; //Reverse month & day because americans are backwards
FSTtimePointer [1] = time[4];
FSTtimePointer [2] = time[2];
FSTtimePointer [3] = time[1];
appP->HIST_write_FST_log(SubMin_CFG.OFFSET, (UINT16)historyPointer, FSTtime);
HIST_write_FST_log的原型是
void (*HIST_write_FST_log) (UINT8 hist_pt_index, UINT16 log_index, FLOAT value);
我得到的编译器警告是:
876: C1000 (W) Illegal pointer assignment
876: C1024 (W) First operand of "=" is not lvalue
如果有人对我使用的编译器感兴趣,那就是日立处理器的瑞萨H8。
您可以使用以下修改代码
FSTtimePointer =(UINT8 *)&FSTtime;
您确定这是您要存储时间的方式吗? 浮点数据类型的内部通常不按字节屏障对齐,并且日期通常是从纪元开始的秒或毫秒(通常为UINT32
或UINT64
),而不是浮点类型。 您可能还需要考虑处理器中MSB或LSB字节的顺序。 (免责声明:我不知道日立处理器如何处理字节顺序或浮点数据类型。)
如果确定这是您想要的方式,则应该能够使用union
来寻址较大数据类型中的各个字节:
union converter_type
{
UNIT8 elements[4];
FLOAT whole;
} converter;
UINT8 time[6];
FLOAT FSTtime = 0; //32bit float
//Get the current time as 6 bytes {secs,mins,hours,day,month,year}
returnSize = appP->DB_get_param_value(12, 0, 8, &time);
if (returnSize < 6) return;
//Pack 4 bytes of time data into a "float"
converter.elements[0] = time[3]; //Reverse month & day because Americans are backwards
converter.elements[1] = time[4]; // (Yes, we are.)
converter.elements[2] = time[2]; // (But what about Canadians? They're "American", too! ;) )
converter.elements[3] = time[1];
FSTtime = converter.whole;
appP->HIST_write_FST_log(SubMin_CFG.OFFSET, (UINT16)historyPointer, FSTtime);
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.