sprintf

#include <stdio.h>
#include <string.h>
char s[10];


int main()
{
    unsigned char chIn[10] = {255, 12, 13, 14, 15, 16, 17, 18, 19, 1};
    char chOut[10] = {0};
    for (int i = 0; i < 10; i++)  
    {
        sprintf(chOut + i * 2, "%02x", chIn[i]); 
    }
printf("%s\n", chOut);


return 0;
}

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