I have problem. The user types a command, which is stored in the cmd variable. The first four characters in the command are non-variable. I retrieve all characters starting from the fourth one. The retrieved characters are passed to the variable check.

This is where the biggest problem arises. I would like to make it so that the program checks for a valid string. The only valid string is |3| but there can be many such strings, for example |4|30| or |15|1|100| and so on to infinity. The most important thing is that the user between two | characters can only enter numbers in decimal format.

I have created a regex, but it doesn't work because even the decimal number alone without the | characters gives a positive result. For there to be a positive result there must be two | characters and a decimal number between them. How can I make the program work properly?

#include "stdarg.h"
#include "string.h"
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <regex.h>

int main()
{
    char cmd[] = "WBRA|5|80|120|3|40|";
    int length = strlen(cmd);
    char check[100];
    int index = 0;
    
    for(int i=4; i<length; i  ){
        check[index  ] = cmd[i];
    }
    
    printf("%s\n\r", check);
    regex_t regex;
    int return_value;
    return_value = regcomp(&regex,"(\\|\\d*\\|){n}",0);
    return_value = regexec(&regex, "check", 0, NULL, 0);
    printf("Result %d\n\r", return_value); // 0 is correct

}

CodePudding user response：

You need to change the two lines in your code to

return_value = regcomp(&regex,"^\\|([0-9] \\|) $",REG_EXTENDED);
return_value = regexec(&regex, check, 0, NULL, 0);

See the C demo.

Details:

• The regex must be ^\|([0-9] \|) $ that matches a whole string that starts with a | char and then contains one or more occurrences of one or more digits and a | char till the end
• REG_EXTENDED is required for this pattern to work correctly
• You used "check" rather than check in the regexec command (so you were checking the regex against check word and not the |5|80|120|3|40| string).