How to iterate through a char ** variable - c

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);
}