How to iterate through a char ** variable

Question

I'm running a small rpc program/ using an rpc framework that takes a char[] from the client file and sends it to the server that enumerates the integers in the string.

I have a file client.c that takes user input and passes it to an external function in a header file.

#include <rpc/rpc.h>
#include "getNumInt.h"

int main(int argc, char **argv){
    CLIENT *cli;
    char *server;
    server = argv[1];

    cli = clnt_create(server, GETNUMINT, GNUMINT, "tcp"); //creates a client handle
    /*does some check for whether the client connected*/
    char command[256];
    int *numInt;
    fgets(command, 256, stdin); 
    numInt = enumints_1(&command, cli); //segfaults here according to backtrace
    return(0);
}

The function enumints_1 is defined in my server stub server.c as:

int *enumints_1(msg, req)
    char **msg; struct svc_req *req;{
    printf(*msg);
    static int numDigits = 0;
    char msgcopy[256];
    strcpy(msgcopy, *msg);
    int i = 0;
    for(i; i<strlen(msgcopy); i++){
        if(msgcopy[i] >= '0' && msgcopy[i] <='9'){
            numDigits++;
        }
    }
    return(&numDigits);
}

My main issue is how I iterate through the char **msg as that is likely why my program is segfaulting. command is just a string taken from user input and then passed by reference to the enumints_1 function. Since it is a pointer to a point I assumed that I could just strcpy or memcpy to copy the string to a char array, but that doesn't work.

also my .x file:

struct intStringPair{
    int numInts;
    char msg[256];
};

program GETNUMINT{
    version GNUMINT{
        int ENUMINTS(string) = 1; //string considered char * the rpc generated file makes it so enumints_1 then has to take char **
        int WRITEMESSAGE(intStringPair) = 2;
    } = 1;
}= 0x20000001;

Answer 1

Like @user3386109 said:

command is not a pointer. So &command is not a pointer-to-a-pointer

so assigning &command to msg is not valid (and my compiler doesn't even compile it)

When I compile this code:

// my set up code

#include <stdio.h>
#include <string.h>
struct svc_req {};
typedef struct svc_req CLIENT;
struct svc_req *clnt_create(const char *, int, int, const char*) {return 0;}
int GETNUMINT=0, GNUMINT=0;

// your code verbatim

int *enumints_1(char **msg, struct svc_req *req){
    printf(*msg);
    static int numDigits = 0;
    char msgcopy[256];
    strcpy(msgcopy, *msg);
    int i = 0;
    for(i; i<strlen(msgcopy); i++){
        if(msgcopy[i] >= '0' && msgcopy[i] <='9'){
            numDigits++;
        }
    }
    return(&numDigits);
}

int main(int argc, char **argv){
    CLIENT *cli;
    char *server;
    server = argv[1];

    cli = clnt_create(server, GETNUMINT, GNUMINT, "tcp"); //creates a client handle
    /*does some check for whether the client connected*/
    char command[256];
    int *numInt;
    fgets(command, 256, stdin); 
    numInt = enumints_1(&command, cli); //segfaults here according to backtrace
    return(0);
}

The compiler says:

<source>: In function 'int main(int, char**)':
<source>:34:25: error: cannot convert 'char (*)[256]' to 'char**'
     numInt = enumints_1(&command, cli); //segfaults here according to backtrace
                         ^~~~~~~~
<source>:10:24: note:   initializing argument 1 of 'int* enumints_1(char**, svc_req*)'
 int *enumints_1(char **msg, struct svc_req *req){
                 ~~~~~~~^~~
Compiler returned: 1

What you can do instead is make a pointer to the array and then pass the address of that:

// my set up code
#include <stdio.h>
#include <string.h>
struct svc_req {};
typedef struct svc_req CLIENT;
struct svc_req *clnt_create(const char *, int, int, const char*) {return 0;}
int GETNUMINT=0, GNUMINT=0;

// your code verbatim
int *enumints_1(char **msg, struct svc_req *req){
    printf(*msg);
    static int numDigits = 0;
    char msgcopy[256];
    strcpy(msgcopy, *msg);
    int i = 0;
    for(i; i<strlen(msgcopy); i++){
        if(msgcopy[i] >= '0' && msgcopy[i] <='9'){
            numDigits++;
        }
    }
    return(&numDigits);
}

int main(int argc, char **argv){
    CLIENT *cli;
    char *server;
    server = argv[1];

    cli = clnt_create(server, GETNUMINT, GNUMINT, "tcp"); //creates a client handle
    /*does some check for whether the client connected*/
    char command[256], *command_pointer=command;
    int *numInt;
    fgets(command, 256, stdin); 
    numInt = enumints_1(&command_pointer, cli); //segfaults here according to backtrace
    return(0);
}