String to Dynamic Byte array

Question

I'm new in Arduino stuck in String to a dynamic byte array.

My String:

String Finalval="6D616320747820636E662031352033300D0A";

Dynamic Byte array:

byte ft[]={0x6D,0x61,0x63,0x20,0x74,0x78,0x20,0x63,0x6E,0x66,0x20,0x31,0x35,0x20,0x33,0x30,0x0D,0x0A};

Answer 1

Common C-string to byte array functions as shown in https://stackoverflow.com/questions/3408706/hexadecimal-string-to-byte-array-in-c work perfectly fine.

Source hex string: 6D616320747820636E662031352033300D0A
Conversion OK buff 0x289 len 18
output byte array:
 00 6d 61 63 20 74 78 20 63 6e 66 20 31 35 20 33 30 mac tx cnf 15 30
 10 0d 0a ..

#include <Arduino.h>
void hexDump (const char *desc, const void *addr, const int len);
bool convert_hexstr_to_bytearray(const char* source, uint8_t* &output,
 size_t& output_len) {
 size_t len = strlen(source);
 //cannot convert non-even string length
 if ((len % 2) != 0) {
 return false;
 }
 //dynamically allocate output buffer
 output_len = len / 2;
 output = (uint8_t*) malloc(output_len);
 const char* curPos = source;
 for (size_t count = 0; count < len; count++) {
 sscanf(curPos, "%2hhx", output + count);
 curPos += 2;
 }
 return true;
}
String Finalval="6D616320747820636E662031352033300D0A";
void setup() {
 Serial.begin(115200);
 Serial.print("Source hex string: ");
 Serial.println(Finalval);
 Serial.flush();
 uint8_t* buffer = nullptr;
 size_t buffer_len = 0;
 if(convert_hexstr_to_bytearray(Finalval.c_str(), buffer, buffer_len)) {
 Serial.println("Conversion OK buff 0x" + String((long)buffer,HEX) + " len " + String(buffer_len));
 hexDump("output byte array", buffer, buffer_len);
 } else {
 Serial.println("Conversion failed\n");
 }
 //free memory
 if(buffer)
 free(buffer);
}
void loop() {
}
void PrintHex8(const uint8_t *data, uint8_t length) // prints 8-bit data in hex
{
 char tmp[length*2+1];
 byte first;
 byte second;
 for (int i=0; i<length; i++) {
 first = (data[i] >> 4) & 0x0f;
 second = data[i] & 0x0f;
 // base for converting single digit numbers to ASCII is 48
 // base for 10-16 to become lower-case characters a-f is 87
 // note: difference is 39
 tmp[i*2] = first+48;
 tmp[i*2+1] = second+48;
 if (first > 9) tmp[i*2] += 39;
 if (second > 9) tmp[i*2+1] += 39;
 }
 tmp[length*2] = 0;
 Serial.print(tmp);
}
void hexDump (const char *desc, const void *addr, const int len) {
 int i;
 unsigned char buff[17];
 const unsigned char *pc = (const unsigned char*)addr;
 // Output description if given.
 if (desc != NULL) {
 Serial.print (desc);
 Serial.println(":");
 }
 if (len == 0) {
 Serial.print(" ZERO LENGTH\n");
 return;
 }
 if (len < 0) {
 Serial.println(" NEGATIVE LENGTH: " + String(len));
 return;
 }
 // Process every byte in the data.
 for (i = 0; i < len; i++) {
 // Multiple of 16 means new line (with line offset).
 if ((i % 16) == 0) {
 // Just don't print ASCII for the zeroth line.
 if (i != 0) {
 Serial.print (" ");
 Serial.println((char*)buff);
 }
 // Output the offset.
 Serial.print (" ");
 PrintHex8((uint8_t*)&i, 1);
 }
 // Now the hex code for the specific character.
 Serial.print(" ");
 PrintHex8(pc + i,1);
 // And store a printable ASCII character for later.
 if ((pc[i] < 0x20) || (pc[i] > 0x7e))
 buff[i % 16] = '.';
 else
 buff[i % 16] = pc[i];
 buff[(i % 16) + 1] = '0円';
 }
 // Pad out last line if not exactly 16 characters.
 while ((i % 16) != 0) {
 Serial.print (" ");
 i++;
 }
 // And print the final ASCII bit.
 Serial.print (" ");
 Serial.println((char*)buff);
}

• Vikash Singh: I'm trying this but not working Serial.write(buffer,sizeof(buffer))
• user3629249: @VikashSingh, there is no statement: Serial.write(buffer,sizeof(buffer)) anywhere in the posted code.
• Maximilian Gerhardt: @VikashSingh sounds like you're having an advanced problem when handling the decoded buffer. What is the exact code?
• Vikash Singh: @MaximilianGerhardt thanks for help my problem solved