I have an array of characters like:
char bytes[8]={2,0,1,3,0,8,1,9}
I want to take the first four chars from this array below, and put them into a new integer variable. How can I do this? I am trying to shift them, but this logic is not working. Any idea? Thanks.
Example: from this array to get: year month day
char bytes[8]={2,0,1,3,0,8,1,9}
int year = 2013 ...... month = 8 ............ day = 19
Instead of left shifting with << operator (which is more or less equivalent to multiplying by 2^N), you should rather multiply by 10^N. Here is how you can do:
int year = bytes[0] * 1000 +
bytes[1] * 100 +
bytes[2] * 10 +
bytes[3];
int month = bytes[4] * 10 +
bytes[5];
int day = bytes[6] * 10 +
bytes[7];
Of course, you can use loops to make your code more readable (if necessary).
enum {
NB_DIGITS_YEAR = 4,
NB_DIGITS_MONTH = 2,
NB_DIGITS_DAY = 2,
DATE_SIZE = NB_DIGITS_YEAR + NB_DIGITS_MONTH + NB_DIGITS_DAY
};
struct Date {
int year, month, day;
};
int getDateElement(char *bytes, int offset, int size) {
int power = 1;
int element = 0;
int i;
for (i = size - 1; i >= 0; i--) {
element += bytes[i + offset] * power;
power *= 10;
}
return element;
}
struct Date getDate(char *bytes) {
struct Date result;
result.year = getDateElement(bytes, 0, NB_DIGITS_YEAR);
result.month = getDateElement(bytes, NB_DIGITS_YEAR, NB_DIGITS_MONTH);
result.day = getDateElement(bytes, NB_DIGITS_YEAR + NB_DIGITS_MONTH, NB_DIGITS_DAY);
return result;
}
With this last code it is easier to change the format of the date stored in bytes.
Example:
int main(void) {
char bytes[DATE_SIZE] = {2, 0, 1, 3, 0, 8, 1, 9};
struct Date result = getDate(bytes);
printf("%02d/%02d/%04d\n", result.day, result.month, result.year);
return 0;
}
Output:
19/08/2013
Do you want this?
int year = byte[0] * 1000 + byte[1] * 100 + byte[2] * 10 + byte[3];
int mounth = byte[4] * 10 + byte[5];
int day = byte[6] * 10 + byte[7];
Note: This works because the integers are actual digit values, not the character codes of the digits like e.g byte[] value at index=0 is 2 but not '2'.
So suppose if you have array of char values like:
char bytes[8]={'2', '0', '1', '3', '0', '8', '1', '9'};
Then change this code like:
#define digit(d) ((d) - ('0'))
int year = digit(byte[0]) * 1000 +
digit(byte[1]) * 100 +
digit(byte[2]) * 10 +
digit(byte[3]);
int mounth = digit(byte[4]) * 10 + digit(byte[5]);
int day = digit(byte[6]) * 10 + digit(byte[7]);
sizeof('a'), sizeof(int), sizeof(char). I written that '2' is char constant that is technically incorrect (because its int not char!). Also a C implementation free to use any encoding (not only ASCII) so H2CO3 writes character codes of the digits.Start with zero. Add the first digit. Multiply with ten. Add the second digit. Multiply by ten. Add the third digit. Multiply by ten. Add the fourth digit. Now you have a four digit integer.
I am unfamiliar with specific c syntax, but I can convey the idea. Concatenate the chars together to form a string, and then use a parseInt method (assuming c has one) to get an integer from that. Alternatively, you could shift the characters through multiplication by powers of 10. For example, given {2,0,1,3}: (2 * 10^3) + (0 * 10^2) + (1 * 10^1) + (3 * 10^0)
Something like this will work:
int month;
int year;
int year = ((int)bytes[0]*1000);
year += (int)bytes[1]*100);
year += ((int)bytes[2] *10);
year += ((int)bytes[3]);
if(sizeof(bytes) == 9){
//month is >10
month = ((int)bytes[4] *10);
month += ((int)bytes[5]);
}
..etc
Here is another way to do this, largely using string functions from the standard library.
I haven't tested this code, but it should give you an idea.
#include <string.h>
int main (void) {
char bytes[8]={2,0,1,3,0,8,1,9};
char tempstring[8], * end;
unsigned int i, year, month, day;
char zero = "0"; //we need to know the difference between 0 and "0"
for (i = 0; i < 8; i++) {
bytes[i] += (int)zero;
}
//now the numbers are the equivalent characters, but we need to split them out
//and convert them
strncopy(tempstring, bytes, 4);
year = strtoul(tempstring, &end, 10);
strncopy(tempstring , bytes + 4, 2);
month = strtoul(tempstring, &end, 10);
strncopy(tempstring , bytes + 6, 2);
day = strtoul(tempstring, &end, 10);
return 0;
}
charis acharand nothing else.charis an integer-type per the standard. So is anint. But that's long way off from saying anintand acharare synonymous. That would be like saying an apple is a fruit, and so is an orange, so apples are oranges (which reminds me, its lunchtime here).