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1. String to Hexadecimal

Code implementation:

void StrToHex(char *pbDest, char *pbSrc, int nLen)
{
  char h1,h2;
  char s1,s2;
  int i;

    for (i=0; i<nLen/2; i++)
    {
        h1 = pbSrc[2*i];
        h2 = pbSrc[2*i+1];

        s1 = toupper(h1) - 0x30; //toupper converts to uppercase
        if (s1 > 9)
            s1 -= 7;
        s2 = toupper(h2) - 0x30;
        if (s2 > 9)
            s2 -= 7;

        pbDest[i] = s1*16 + s2;
    }
}

2. Hexadecimal to String

Code implementation:

void HexToStr(char *pszDest, char *pbSrc, int nLen)
{
    char ddl, ddh;
    for (int i = 0; i < nLen; i++)
    {
        ddh = 48 + pbSrc[i] / 16;
        ddl = 48 + pbSrc[i] % 16;
        if (ddh > 57) ddh = ddh + 7;
        if (ddl > 57) ddl = ddl + 7;
        pszDest[i * 2] = ddh;
        pszDest[i * 2 + 1] = ddl;
    }
    pszDest[nLen * 2] = '\0';
}

Or

u16 Hex2StringArray (u8 *pSrc,  u16 SrcLen, u8 *pObj)
{
    u16 i=0;

    for(i=0;    i<SrcLen;   i++)
    {
        sprintf((char *)(pObj + i * 2), "%02X", *(pSrc + i));
    }
    *(pObj + i * 2) = '\0';
    return  (i * 2);
}

Effect: Hexadecimal: 0x13 0xAA 0x02 to string: “13AAA2”

3. String to Decimal

Code implementation:First method, if it has a negative sign this is the implementation of the atoi function:

int my_atoi(const char *str)
{
    int value = 0;
    int flag = 1; // Determine the sign
    while (*str == ' ')  // Skip spaces at the beginning of the string
    {
        str++;
    }
    if (*str == '-')  // If the first character is '-', it may be negative
    {
        flag = 0;
        str++;
    }
    else if (*str == '+') // If the first character is '+', it may be positive
    {
        flag = 1;
        str++;
    }// If the first character is not '+' or '-' and not a digit, return 0 directly
    else if (*str >= '9' || *str <= '0') 
    {
        return 0;    
    }
    // End conversion when encountering a non-digit character or '
'
    while (*str != '\0' && *str <= '9' && *str >= '0')
    {
        value = value * 10 + *str - '0'; // Convert digit character to corresponding integer
        str++;
    }
    if (flag == 0) // For negative numbers
    {
        value = -value;
    }
    return value;
}

Effect: String: “-123” to -123Second method, if without a negative sign:

void StrtoDec(uint32_t *pbDest, char *pbSrc, int nLen)
{
    int i;
    int tmp=0;
    if(nLen > 10)
        *pbDest = 0;
    tmp = 1;
    *pbDest = 0;
    for (i=nLen-1; i>=0; i--)
    {
        *pbDest += tmp*(*(pbSrc+i)-'0');
        tmp = tmp*10;
    }
}

Effect: String: “123” to 123Third method: Includes conversion to floating point:

//m^n function
//Return value: m^n power.
u32 NMEA_Pow(u8 m,u8 n)
{
    u32 result=1;    
    while(n--)result*=m;    
    return result;
}
//str converts to number, ends with ',' or '*'
//buf: number storage area
//dx: decimal point position, returned to the calling function
//Return value: converted value
int NMEA_Str2num(u8 *buf,u8*dx)
{
    u8 *p=buf;
    u32 ires=0,fres=0;
    u8 ilen=0,flen=0,i;
    u8 mask=0;
    int res;
    while(1) // Get the length of integer and decimal
    {
        if(*p=='-'){mask|=0X02;p++;}// Is negative
        if(*p==','||(*p=='*'))break;// Encountered end
        if(*p=='.'){mask|=0X01;p++;}// Encountered decimal point
        else if(*p>'9'||(*p<'0'))   // Invalid character
        {   
            ilen=0;
            flen=0;
            break;
        }   
        if(mask&0X01)flen++;
        else ilen++;
        p++;
    }
    if(mask&0X02)buf++; // Remove negative sign
    for(i=0;i<ilen;i++) // Get integer part data
    {  
        ires+=NMEA_Pow(10,ilen-1-i)*(buf[i]-'0');
    }
    if(flen>5)flen=5;   // Take at most 5 decimal places
    *dx=flen;           // Decimal point position
    for(i=0;i<flen;i++) // Get decimal part data
    {  
        fres+=NMEA_Pow(10,flen-1-i)*(buf[ilen+1+i]-'0');
    } 
    res=ires*NMEA_Pow(10,flen)+fres;
    if(mask&0X02)res=-res;         
    return res;
} 

Effect: String: “123.456” first converted to 123456, then divided by 1000 to get 123.456

4. Decimal to String

Code implementation:If it is just a single decimal to string, use sprintf function.If it is a decimal array:

u16 DectoStr (u8 *pSrc, u16 SrcLen, u8 *pObj)
{
    u16 i=0;

    for(i=0;    i<SrcLen;   i++)
    {
        sprintf((char *)(pObj + i * 2), "%02d", *(pSrc + i));
    }
    *(pObj + i * 2) = '\0';
    return  (i * 2);
}

Effect: Decimal array 13 14 to string “1314”

5. u8, u32 Conversion

For example: In ASCII code Here is the description of the image Character ‘A’, one byte 8bit, which is u8 hexadecimal 0x41 binary 0100 0001And the corresponding decimal is 65 integer 65, 4 bytes 32bit, which is u32 hexadecimal 0x41 binary 0000 0000 0000 0000 0000 0000 0100 0001Convert u32 number to u8 arrayNote: Here is a character array, not a stringA string is a char array terminated with a null character (\0)

void U32ToU8Array(uint8_t *buf, uint32_t u32Value)
{
    buf[0] = ((u32Value >> 24) & 0xFF);
    buf[1] = ((u32Value >> 16) & 0xFF);
    buf[2] = ((u32Value >> 8) & 0xFF);
    buf[3] = (u32Value & 0xFF);
}

Effect: Integer 50 to character array {‘\0′,’\0′,’\0′,’2’}u8 array to u32

void U8ArrayToU32(uint8_t *buf, uint32_t *u32Value)
{
    *u32Value = (buf[0] <<24) + (buf[1] <<16) + (buf[2] <<8) + (buf[3] <<0);
}

Effect: Character array {‘\0′,’\0′,’\0′,’2’} to integer 50

6. Big Endian and Little Endian

Finally, there is the big-endian and little-endian issue. STM32 defaults to little-endian mode, so how to convert to big-endian?1. Convert to big-endian

For big-endian:
pPack[0] = (u8)((len >> 8) & 0xFF);
pPack[1] = (u8)(len & 0xFF);

For little-endian:
pPack[0] = (u8)(len & 0xFF);
pPack[1] =  (u8)((len >> 8) & 0xFF);

Effect: len is a data type u16 (short), for example 0x11 0x22, converted to u8 (unsigned char) array.Big-endian:

pPack[0] (0x11 ) 
pPack[1] (0x22) 

Little-endian:

pPack[0] (0x22) 
pPack[1] (0x11)

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