• C

# Byte swapping a double in C / C++

Hi, im converting a program from a silicon graphics machine to the PC.

I would like to know how to byte swap a double

I have tried the following but it doesnt seem to work :-

-----------------------------------------------
void byteSwapDouble(double *ptrValue)
{
double  *ptrTemp;
char * swapA, swapB;

ptrTemp = ptrValue;
swapA = (char *)ptrTemp;

swapB = swapA[0];
swapA[0] = swapA[7];
swapA[7] = swapB;
swapB = swapA[1];
swapA[1] = swapA[6];
swapA[6] = swapB;
swapB = swapA[2];
swapA[2] = swapA[5];
swapA[5] =swapB;
swapB = swapA[3];
swapA[3] = swapA[4];
swapA[4] = swapB;

ptrTemp = (double *)swapA;
ptrValue = ptrTemp;
}
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Commented:
#define swapByte(a, b, t) t=*(a); *(a)=*(b); *(b)=t

void byteSwapDouble(double *ptrValue)
{
char temp;
swapByte(ptrValue, ptrValue+7, temp);
swapByte(ptrValue+1, ptrValue+6, temp);
swapByte(ptrValue+2, ptrValue+5, temp);
swapByte(ptrValue+3, ptrValue+4, temp);
}
0
Commented:

#define swapByte(a, b, t) t=*(a); *(a)=*(b); *(b)=t

void byteSwapDouble(double *ptrValue)
{
char temp; char *ptr = ptrvalue;

swapByte(ptr, ptr+7, temp);
swapByte(ptr+1, ptr+6, temp);
swapByte(ptr+2, ptr+5, temp);
swapByte(ptr+3, ptr+4, temp);
}
0

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Author Commented:
Good stuff.
0
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