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POC - creating a packet using char and int
 

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  1. POC - creating a packet using char and int
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    <p>I'm looking to build a binary string that consists of hex values... I've learned sprintf is not the correct way to accomplish this. I've got a real simple gui to collect configuration settings that need to be sent a device. The values can be signed and will always be numerical. I have a set of values like:</p> <pre><code>#define PKTHEAD 0xA5 #define VALONE 0xA0 #define VALTWO 0xA1 #define VALTHREE 0xA2 #define PKTTAIL 0x5A signed int val1 = 10000; //0x2710 signed int val2 = -84; //0xFFAC signed int val3 = -175001 //0xFFFD5467 </code></pre> <p>My end goal is to have a packet that would resemble "PKTHEAD|PKTHEAD|PKTHEAD|VALONE|val1|VALTWO|val2|VALTHREE|val3|PKTTAIL|PKTTAIL|PKTTAIL", and the hex representation would be A5A5A5A000002710A1FFFFFFACA2FFFD54675A5A5A. </p> <p>Right now I'm doing this:</p> <pre><code>int main(int argc, char *argv[]) { int numBytes = 10; signed char *tmp; signed char *pyld; pyld = calloc(numBytes, sizeof(char)); signed int val1 = 10000; //0x2710 signed int val2 = -84; //0xFFAC signed int val3 = -175001 //0xFFFD5467 tmp = pyld; *(tmp + (numBytes - 1)) = DACHEAD; *(tmp + (numBytes - 2)) = DACHEAD; *(tmp + (numBytes - 3)) = DACHEAD; *(tmp + (numBytes - 4)) = VALONE; *(tmp + (numBytes - 5)) = val1; printf("payload = %hhx%hhx%hhx%hhx%hx%hx%hhx%hx\n", pyld[9], pyld[8], pyld[7], pyld[6], pyld[5], pyld[4], pyld[3], pyld[2], pyld[1], pyld[0]); } </code></pre> <p>The output is: "payload = a5a5a5a0100a1ffac"</p> <p>My val1 value is incorrect and I'm wondering if there is a better way to compose this packet. Should I be doing bit shifts instead?</p> <p>Any help is greatly appreciated.</p> <p>Thanks!</p>
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