Convert hex string (char []) to int?

Question

I have a char[] that contains a value such as \"0x1800785\" but the function I want to give the value to requires an int, how can I convert this to an int? I have searched a

Answer 1

Have you tried strtol()?

strtol - convert string to a long integer

Example:

const char *hexstring = "abcdef0";
int number = (int)strtol(hexstring, NULL, 16);

In case the string representation of the number begins with a 0x prefix, one must should use 0 as base:

const char *hexstring = "0xabcdef0";
int number = (int)strtol(hexstring, NULL, 0);

(It's as well possible to specify an explicit base such as 16, but I wouldn't recommend introducing redundancy.)

Answer 2

Something like this could be useful:

char str[] = "0x1800785";
int num;

sscanf(str, "%x", &num);
printf("0x%x %i\n", num, num); 

Read man sscanf

Answer 3

I made a librairy to make Hexadecimal / Decimal conversion without the use of stdio.h. Very simple to use :

unsigned hexdec (const char *hex, const int s_hex);

Before the first conversion intialize the array used for conversion with :

void init_hexdec ();

Here the link on github : https://github.com/kevmuret/libhex/

Answer 4

I know this is really old but I think the solutions looked too complicated. Try this in VB:

Public Function HexToInt(sHEX as String) as long
Dim iLen as Integer
Dim i as Integer 
Dim SumValue as Long 
Dim iVal as long
Dim AscVal as long

    iLen = Len(sHEX)
    For i = 1 to Len(sHEX)
      AscVal = Asc(UCase(Mid$(sHEX, i,  1)))
      If AscVal >= 48 And AscVal  <= 57 Then
        iVal  = AscVal - 48
      ElseIf AscVal >= 65 And AscVal <= 70 Then
        iVal = AscVal - 55
      End If 
      SumValue = SumValue + iVal * 16 ^ (iLen- i)
    Next i 
    HexToInt  = SumValue
End Function 

Answer 5

Or if you want to have your own implementation, I wrote this quick function as an example:

/**
 * hex2int
 * take a hex string and convert it to a 32bit number (max 8 hex digits)
 */
uint32_t hex2int(char *hex) {
    uint32_t val = 0;
    while (*hex) {
        // get current character then increment
        uint8_t byte = *hex++; 
        // transform hex character to the 4bit equivalent number, using the ascii table indexes
        if (byte >= '0' && byte <= '9') byte = byte - '0';
        else if (byte >= 'a' && byte <='f') byte = byte - 'a' + 10;
        else if (byte >= 'A' && byte <='F') byte = byte - 'A' + 10;    
        // shift 4 to make space for new digit, and add the 4 bits of the new digit 
        val = (val << 4) | (byte & 0xF);
    }
    return val;
}

Answer 6

Try below block of code, its working for me.

char *p = "0x820";
uint16_t intVal;
sscanf(p, "%x", &intVal);

printf("value x: %x - %d", intVal, intVal);

Output is:

value x: 820 - 2080