Convert array of bytes to uint64_t?

Question

I have a large array of bytes called memory and I'm trying to convert 8 of those bytes to a uint64_t. I'm trying to print the number in big-endian.

I have this so far:

uint64_t value =  (uint64_t)(memory[256]) | //location contains byte 88
   (uint64_t)(memory[257]) << 8  |          //77
   (uint64_t)(memory[258]) << 16 |          //66
   (uint64_t)(memory[259]) << 24 |          //55
   (uint64_t)(memory[260]) << 32 |          //44
   (uint64_t)(memory[261]) << 40 |          //33
   (uint64_t)(memory[262]) << 48 |          //22
   (uint64_t)(memory[263]) << 56;           //11

I print like so:

printf("0x%x", value);

The output is 0x55667788, but I want the output to be 0x1122334455667788.

Any suggestions of how I can fix the above code to print 0x1122334455667788?

Solution: The print statement needed to be:

printf("0x%lx", value);

I dont know abt this.. But i found a similar problem here... http://stackoverflow.com/questions/4142251/convert-array-of-8-bytes-to-signed-long-in-c — Ashwin Golani, Mar 21 '17 at 06:08
%08x didn't work :( but I am getting a warning - "format ‘%x’ expects argument of type ‘unsigned int’, but argument 2 has type ‘uint64_t {aka long unsigned int}’ [-Wformat=] printf("%08x", value);" — jmu_nova, Mar 21 '17 at 06:12
%lx worked! glad to know it was just the print statement. Thanks! — jmu_nova, Mar 21 '17 at 06:15
_I'm trying to print the number in big-endian._ [Bit-shift are endian independent](http://stackoverflow.com/q/7184789/1606345) — David Ranieri, Mar 21 '17 at 07:00

score 0 · Accepted Answer · answered Mar 21 '17 at 06:27

The format specifier %lx works because the unsigned long type happens to have at least 64 bits on your system. The C Standard does not guarantee that and indeed it has only 32 bits on 64-bit Microsoft Windows. unsigned long long is guaranteed to have at least 64 bits, so you could use this:

printf("0x%llx\n", (unsigned long long)value);

If your compiler and C library support C99 or a later standard, you can use the macros defined in <inttypes.h>:

printf("0x%" PRIx64 "\n", value);

Convert array of bytes to uint64_t?

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