How to check if String consist of numeric or alphabet in C

Question

I need some help in Identifying the string. I have incoming string like this *H1999999#it can vary from *H1000000#~*H1999999# sometimes it is *H1FINE# or *H1MED# or any other text in between.Now what I have already done is I have parsed the numeric string and copied the integer value to a buffer. Here is the code for that.

        char H1subbuff[10];

        char *ptr;

        if ((strncmp(rec,"*H1", 3) == 0) && (rec[9] == '#'))    
         {
            memcpy(H1subbuff, &rec[3], 6 );
            H1subbuff[6] = '\0';

            H1Val = strtol(H1subbuff, &ptr, 10);

            //Display H1VAL
       }

Now my query is how can check if the String consist of Number or Alphabet. How can I check H1subbuff data, so that I can compare. I need to do the same above process of parsing *H1FINE# string.

Note :- The above two string doesn't have same string length.

Answer 1

You can use this to determine whether it's numeric or not

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void
check_string(const char *string)
{
    char *endptr;
    long int value;
    if (strstr(string, "*H1") == NULL)
        return; // This string is not valid
    // Move after the '*H1'
    string += 3;
    if (strchr(string, '#') == NULL)
        return; // Missing the '#'
    // Now we can try to determine whether the content
    // between '*H1' and '#' is a number, or text
    value = strtol(string, &endptr, 10);
    // This simply compares pointer values, if `endptr'
    // has the same value as `string`, then `strtol()' didn't
    // find any numeric character, i.e. the first one
    // in the data pointed to by `string' was non-numeric
    if (endptr == string)
        fprintf(stdout, "It's NOT a number\n");
    else if (*endptr == '#')
        fprintf(stdout, "It's a number: %ld\n", value);
    else
        fprintf(stdout, "It's almost a number\n");
}

First we perform some integrity check, once we know that it's a candidate we can try to determine whether or not the delimited portion is a number or not.

Note the "It's almost a number" part, it means that not all the characters delimited by *H1 and # are numeric, but the few first were and then a non numeric character occurred.

Also, if it was allowed to have a '#' embedded into the delimited portion, escaping it for example, this code would not work.

Answer 2

like this:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <stdbool.h>

bool validate_data(const char rec[], int *number, char text[]){
    *number = -1;//if invalid
    *text = 0;   //if invalid

    if(strncmp(rec, "*H1", 3) != 0) return false;//invalid header

    bool not_digit = false;
    int i, j = 0;
    for(i = 3; rec[i] && rec[i] != '#'; ++i){
        text[j++] = rec[i];
        if(!isdigit(rec[i]))
            not_digit = true;
    }
    text[j] = 0;

    if(rec[i] != '#'){
        *text = 0;
        return false;//invalid footer
    }
    if(not_digit == false){
        if(j != 6){
            *text = 0;//valid as text?
            return false;//invalid number format
        }
        *number = atoi(text);
    }
    return true;
}


int main(void){
    const char *test_data[] = {
        "*H1000000#","*H1999999#", "*H1123456#", "*H1FINE#", "*H1MED#",
        "*h123#", "**H1666666#", "*H2888888#", "*H1777#", "*H1555555"
    };
    int number_of_data = sizeof(test_data)/sizeof(*test_data);
    char H1subbuff[10];
    int H1Val;

    for(int i = 0; i < number_of_data; ++i){
        printf("%s :\n", test_data[i]);
        if(validate_data(test_data[i], &H1Val, H1subbuff)){
            if(H1Val >= 0)
                printf("value is %d(%s)\n", H1Val, H1subbuff);
            else
                printf("text is %s\n", H1subbuff);
        } else {
            printf("invalid format\n");
        }
        puts("");
    }
    return 0;
}

Answer 3

If you have only two input strings as said in the question you can directly compare them and do the action accordingly.

And if not this case then you can use the ASCII values to compare the characters in the string .