CODEWITHSUNDEEP
cstringhex
Allamaprabhu
Allamaprabhu

Reputation: 865

How to convert string to hex value in C

I have string "6A" how can I convert into hex value 6A?

Please help me with solution in C

I tried 

char c[2]="6A"
char *p;
int x = atoi(c);//atoi is deprecated 

int y = strtod(c,&p);//Returns only first digit,rest it considers as string and
//returns 0 if first character is non digit char.

Upvotes: 26

Views: 139857

Answers (2)

Jarrett GXZ
Jarrett GXZ

Reputation: 608

For converting string to hex value, and storing to variable:

char text[20] = "hello friend";

int text_len = strlen(text);
char *hex_output = malloc(text_len*2 + 1); // 2 hex = 1 ASCII char + 1 for null char

if (hex_output == NULL)
{
        perror("Failed to allocated memory.");
        return 1;
}

int hex_index = 0;

for (int i = 0; i < strlen(text); i++)
{
        char t = text[i];

        int w = sprintf(&hex_output[hex_index], "%x", t);

        if (w < 0)
        {
                perror("Failed to convert to hex.");
                return 1;
        }

        hex_index += 2;
}

hex_output[strlen(hex_output)] = 0x0;
printf("%s\n", hex_output);

Output:

68656c6c6f20667269656e64

Upvotes: 0

Weather Vane
Weather Vane

Reputation: 34575

The question

"How can I convert a string to a hex value?"

is often asked, but it's not quite the right question. Better would be

"How can I convert a hex string to an integer value?"

The reason is, an integer (or char or long) value is stored in binary fashion in the computer.

"6A" = 01101010

It is only in human representation (in a character string) that a value is expressed in one notation or another

"01101010b"   binary
"0x6A"        hexadecimal
"106"         decimal
"'j'"         character

all represent the same value in different ways.

But in answer to the question, how to convert a hex string to an int

char hex[] = "6A";                          // here is the hex string
int num = (int)strtol(hex, NULL, 16);       // number base 16
printf("%c\n", num);                        // print it as a char
printf("%d\n", num);                        // print it as decimal
printf("%X\n", num);                        // print it back as hex

Output:

j
106
6A

Upvotes: 64

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