any solution to convert given char*(number) to required unsigned char*(hex of number)

Given For e.g,
char input[] = "10011210582553796";

now Hexadecimal of 10011210582553796 is 2391249A8B74C4.

So output unsigned char* should have value,
unsigned char output[8] = {0x00,0x23,0x91,0x24,0x9A,0x8B,0x74,0xC4};

can anyone give a solution to convert given input char* to output char* with above mentioned requirement.

code should run on platform, for which __int64/signed long long is not supported.

Thanx in advance...