For example i have a string about time like 134058 (hhmmss). What is the best way to parse and handle this data? I think i can do this with strncmp or some loops but i am not sure if it's the logical or efficant way.

And what kind of data type should i keep these variable with?

CodePudding user response：

There are some functions in stdlib.h, atoi and strtol, which can not be used here.

Therefore, sticking with the answers from the comments is best.

#include <stdio.h>
#include <string.h> // for strlen
#include <ctype.h> // for isdigit

enum {TIME_LENGTH = 6};

int main(void) {
    int hours, minutes, seconds;
    char *input_string = "134058";

    if (strlen(input_string) != TIME_LENGTH) {
        return 1; // wrong length
    }

    for (int i = 0; i < TIME_LENGTH; i  ) {
        if (input_string[i] < '0' || input_string[i] > '9') {
            return 1; // element not a digit
        }
    }

    // just for completeness, seems like an overkill here
    for (int i = 0; i < TIME_LENGTH; i  ) {
        if (!isdigit(input_string[i])) {
            return 1; // element not a digit
        }
    }

    // straight way, drop '* 1' if used
    hours =   (input_string[0] - '0') * 10   (input_string[1] - '0') * 1;
    minutes = (input_string[2] - '0') * 10   (input_string[3] - '0') * 1;
    seconds = (input_string[4] - '0') * 10   (input_string[5] - '0') * 1;
    printf("Time: d:d:d\n", hours, minutes, seconds);

    // from chux - Reinstate Monica
    sscanf(input_string, "---", &hours, &minutes, &seconds);
    printf("Time: d:d:d\n", hours, minutes, seconds);

    // from Support Ukraine
    hours =   10 * input_string[0]   input_string[1] - 11 * '0';
    minutes = 10 * input_string[2]   input_string[3] - 11 * '0';
    seconds = 10 * input_string[4]   input_string[5] - 11 * '0';
    printf("Time: d:d:d\n", hours, minutes, seconds);

    return 0;
}

$ gcc -Wall parse_simple_time_string.c
$ ./a.out                             
Time: 13:40:58
Time: 13:40:58
Time: 13:40:58
$ 

CodePudding user response：

Depends what you mean by 'best'. Some examples shown already , they will also suit your needs. I prefer generic reusable methods; though of course the choice is up to you depending on how much you will re-use the code.

The following code allows range checking, and invalid string checking , haven't tested fully but once you've written the function once it can be re-used to suit. Any comments welcome.

#include <stdint.h>
#include <stdbool.h>

/**
 * @param str string to parse
 * @param len length of string to parse
 * @param out value pointer
 * @param min minimum allowed value
 * @param max maximum allowed value
 * @return true if parsed correctly, false if parse error
 * @description convert part of a string to decimal number between specified range
 * @example
 * uint32_t hour;
 * // function returns true and sets hour value to 12
 * parseDecimalInt("12345",2,&hour,0,23);
 */
bool parseDecimalInt(const char* str, int32_t len, int32_t* out, int32_t min, int32_t max)
{
    int32_t base = 1;
    // convert string to len
    *out = 0;

    if (strlen(str) < len) // check string is longer than desired string to parse
        return false;

    if (len < 1)
        return false; // invalid string length

    len--;

    while (len >= 0)
    {
        int8_t digit = str[len] - '0';

        if (digit < 0 || digit > 9)
            return false; // invalid number

        *out = *out   (base * digit);
        base *= 10;
        len--;
    }

    // outside bounds checks
    if (*out < min)
        return false;
    if (*out > max)
        return false;

    return true;
}

void main()
{
    int32_t hours, mins, secs;
    const char* str = "123456";
    // Parses TWO characters as decimal starting from ZEROTH character in string
    if (!parseDecimalInt(&str[0], 2, &hours, 0, 23))
    {
        // error parsing hours - print something here and return
    }
    // Parses TWO characters as decimal starting from SECOND character in string
    if (!parseDecimalInt(&str[2], 2, &mins, 0, 59))
    {
        // error parsing mins - print something here and return 
    }
    // Parse TWO characters as decimal starting from FOURTH character in string
    if (!parseDecimalInt(&str[4], 2, &secs, 0, 59))
    {
        // error parsing seconds - print something here and return 
    }
    // if returned on error, hours mins, secs should be valid
    // hours will be 12, mins will be 34, secs will be 56
}