Programming Help Forums / Other Languages / C

Beginner question: string arrays

Arcan — Wed, 05 Oct 2011 08:41:12 GMT

I've just started working on a simple shell-program. Currently reading user input works fine, but I'm having trouble splitting the input string into smaller strings of one word each, stored in the 2d array param. Here's an example of my desired result:

input: "hello my name is bob -f"

param[0] = "hello"
param[1] = "my"
param[2] = "name"
param[3] = "is"
param[4] = "bob"
param[5] = "-f"

So far, my code looks like this:

[quote]#include >stdio.h>
#include >stdlib.h>
#include >ctype.h>
#include >string.h>

#define DEBUG

int split(char *input, char **param)
{
}

int main(void)
{
while (1) {
//Reads input
printf("%s@inf1060-sh>", getenv("USER"));
char input[120];
fflush(stdout);
if (fgets(input, sizeof input, stdin) == NULL) return 0;

#ifdef DEBUG
fprintf(stderr,"%s", input);
#endif

char *param[21];
param[0][0] = 'a';

int emptyIn = split(input, param);
}
}
[/quote]

This is not the entirety of my code, but the crash happens here.

The arrows in the header-inclusions (what do I call them?) are switched around here so the content of them aren't left out.

Now what I'm wondering is:

why does
[quote]param[0][0] = 'a';[/quote]
give segmentation fault?
How do I fix this?

Thanks in advance

Struct Problems storing Client IP-address

studiologe — Thu, 22 Sep 2011 22:03:18 GMT

Hi everyone,
I got stuck again, this time with a different problem though. Writing on a little chat server based on “Beej’s Guide to Network Programming” and I tried to save each incoming connection into an array, so that every time a client posts something that it also will echo the clients IP-address.
For example:
127.0.0.1: Hello, anybody out there?

I got everything working but right now I just display following output:
Socket 4: Hello, anybody out there?

So in order to store the IP addresses as soon as a client connects, I created following struct.

[code]
struct connection
{
const char *IPv4_addr;
};
[/code]

And created an array variable of type struct connection;
[code]
struct connection client[6]; // client information
[/code]

Then I try to store the client IP in this array and I use the following command:
[code]
client[newfd].IPv4_addr=inet_ntop(remoteaddr.ss_family,get_in_addr((struct sockaddr*)&remoteaddr),remoteIP, INET_ADDRSTRLEN);
[/code]

Here is the function it is in
[code]
//----------------------------------------------------------
// CHECK EXISTING CONNECTIONS FOR DATA
//------------------------------------
for(i = 0; i <= fdmax; i++)
{
//------------------------------------------------------
// CHECK FOR NEW CONNECTIONS
//--------------------------
if (FD_ISSET(i, &read_fds)) // we got one!!
{
if (i == listener)
{
// handle new connections
addrlen = sizeof remoteaddr;
newfd = accept(listener,(struct sockaddr *)&remoteaddr,&addrlen);
if (newfd == -1) // If connection attempt fails
{
perror("accept");
}
else
{
FD_SET(newfd, &master); // add to master set
if (newfd > fdmax) // keep track of the max
{
fdmax = newfd;
}
client[newfd].IPv4_addr=inet_ntop(remoteaddr.ss_family,get_in_addr((struct sockaddr*)&remoteaddr),remoteIP, INET_ADDRSTRLEN);
printf("selectserver: new connection from %s on socket %d",
/* -> */ inet_ntop(remoteaddr.ss_family,get_in_addr((struct sockaddr*)&remoteaddr),remoteIP, INET6_ADDRSTRLEN),newfd);
}
}
[/code]

And right in that line where it says:
[code]
client[newfd].IPv4_addr=inet_ntop(remoteaddr.ss_family,get_in_addr((struct sockaddr*)&remoteaddr),remoteIP, INET_ADDRSTRLEN);
[/code]

Is my problem, since I’m using a pointer and it always clear the entire content of that variable as soon as another client connects because it keeps pointing to the same spot in the memory. It works perfectly fine for a single connection (of course…..)
Now I unfortunately can’t change it, since the function I use in that same line requires a pointer at that time I call it.
So what else could I do, to bypass this problem and somehow store each clients IP-address in that client array of type struct connection?

I hope You understand what exactly my problem is.
The entire code is attached in a .zip file.

I really hope you guys can help me out and I’d appreciate each suggestion that leads me the right way, since this is bugging me for a few days now.

Thanks,
~Stud

Infix/postfix & bc and dc conversion

sheepdogg09 — Sun, 18 Sep 2011 17:50:25 GMT

Hi, thank you for taking the time to take a look at this.

So here's the deal, my assignment is to write a program that resembles the traditional version of bc. It will translate the more common way of writing arithmetic expressions into postfix form used by the dc utility.
Ok, so there is plenty of info how to write a program to convert to postfix notation, therefore thats not the issue. The issue being, I can't find any info on the bc/dc utilities, and can't really figure out how they choose their output, other than testing thousands of entries and expressions over and over. Our teacher simply expects us to be pros at the unix environment without any prior knowledge or lessons.

Examples of input and output, respectively.
1+2*3 -- 1 2 3*+ps
i=+2; -- li 2+si
a=b=c=0 -- 0dscdsbsa

if(x<4) -- [ 2sy ]s0
y=2; -- lx 4>0

Thanks for any help you may provide.
Paul

Role of function

SeoDezin — Tue, 09 Aug 2011 17:24:59 GMT

What is role of functions in C++ and how they are used?

Beginner Advice Needed

John Roger — Fri, 15 Oct 2010 04:49:57 GMT

I am Virtual Assistant working for a group of web developer. Because of this kind of task I became interested in programming. Can someone provide me with resources for want to be programmer.

What is the difference between ++var and var++?

myprogramminghelpforum — Sat, 25 Jun 2011 06:11:03 GMT

The ++ operator is called the increment operator. When the operator is placed before the variable (++var), the variable is incremented by 1 before it is used in the expression. When the operator is placed after the variable (var++), the expression is evaluated, and then the variable is incremented by 1.

The same holds true for the decrement operator (--). When the operator is placed before the variable, you are said to have a prefix operation. When the operator is placed after the variable, you are said to have a postfix operation.

For instance, consider the following example of postfix incrementation:

int x, y;x = 1;y = (x++ * 5);

In this example, postfix incrementation is used, and x is not incremented until after the evaluation of the expression is done. Therefore, y evaluates to 1 times 5, or 5. After the evaluation, x is incremented to 2.

Now look at an example using prefix incrementation:

int x, y;x = 1;y = (++x * 5);

This example is the same as the first one, except that this example uses prefix incrementation rather than postfix. Therefore, x is incremented before the expression is evaluated, making it 2. Hence, y evaluates to 2 times 5, or 10.

When is a switch statement better than multiple if statements?

myprogramminghelpforum — Sat, 25 Jun 2011 06:09:59 GMT

A switch statement is generally best to use when you have more than two conditional expressions based on a single variable of numeric type. For instance, rather than the code

if (x == 1)     printf("x is equal to one.");else if (x == 2)     printf("x is equal to two.");else if (x == 3)     printf("x is equal to three.");else     printf("x is not equal to one, two, or three.");

the following code is easier to read and maintain:

switch (x){     case 1:   printf("x is equal to one.");                    break;     case 2:   printf("x is equal to two.");                    break;     case 3:   printf("x is equal to three.");                    break;     default:  printf("x is not equal to one, two, or three.");                    break;}

Notice that for this method to work, the conditional expression must be based on a variable of numeric type in order to use the switch statement. Also, the conditional expression must be based on a single variable. For instance, even though the following if statement contains more than two conditions, it is not a candidate for using a switch statement because it is based on string comparisons and not numeric comparisons:

char* name = "Lupto";if (!stricmp(name, "Isaac"))     printf("Your name means 'Laughter'.");else if (!stricmp(name, "Amy"))     printf("Your name means 'Beloved'. ");else if (!stricmp(name, "Lloyd"))     printf("Your name means 'Mysterious'. ");else     printf("I haven't a clue as to what your name means.");

What is a local block?

myprogramminghelpforum — Sat, 25 Jun 2011 06:09:25 GMT

A local block is any portion of a C program that is enclosed by the left brace ({) and the right brace (}). A C function contains left and right braces, and therefore anything between the two braces is contained in a local block. An if statement or a switch statement can also contain braces, so the portion of code between these two braces would be considered a local block.

Additionally, you might want to create your own local block without the aid of a C function or keyword construct. This is perfectly legal. Variables can be declared within local blocks, but they must be declared only at the beginning of a local block. Variables declared in this manner are visible only within the local block. Duplicate variable names declared within a local block take precedence over variables with the same name declared outside the local block. Here is an example of a program that uses local blocks:

#include <stdio.h>void main(void);void main(){     /* Begin local block for function main() */     int test_var = 10;     printf("Test variable before the if statement: %d", test_var);     if (test_var > 5)     {          /* Begin local block for "if" statement */          int test_var = 5;          printf("Test variable within the if statement: %d",                 test_var);          {               /* Begin independent local block (not tied to                  any function or keyword) */               int test_var = 0;               printf(               "Test variable within the independent local block:%d",               test_var);          }          /* End independent local block */     }     /* End local block for "if" statement */     printf("Test variable after the if statement: %d", test_var);}/* End local block for function main() */

This example program produces the following output:

Test variable before the if statement: 10

Test variable within the if statement: 5

Test variable within the independent local block: 0

Test variable after the if statement: 10

Notice that as each test_var was defined, it took precedence over the previously defined test_var. Also notice that when the if statement local block had ended, the program had reentered the scope of the original test_var, and its value was 10.

Array definition

misfi — Sun, 24 May 2009 06:26:30 GMT

I wrote:

int a[] = {
0,0,1,0,0,
0,1,0,1,0,
1,0,0,0,1,
1,1,1,1,1,
1,0,0,0,1
};

The size of array is a[25] or a[5][5]?
Thx

The best compiler for C

misfi — Sun, 24 May 2009 04:22:39 GMT

The best compiler for C under windows is....?

I use DevC++...

assigning values to pointers inside a structure---urgent help needed!!!!!!!!!

abhisrk — Sun, 15 May 2011 16:45:31 GMT

typedef struct x
{int a;
int b;
int *c;
}test;
i
nt main(void)

{

test.b=a2;
test->c=a2;

printf(" c is %d", test1.c);
}

How to assign a value to c?

How do I read string say -5/-10 and then reduce the first number and second number to lowest terms.?

Nvoron23 — Sun, 13 Mar 2011 03:47:25 GMT

code so far:

#include <stdio.h>
#include <math.h>

typedef struct frac{ /* a fraction, numer/denom */
int numer; /* numerator of fraction */
int denom; /* denominator of fraction */
} frac;

/* greatest common divisor */
int gcd(int a, int b)
{
while (b != 0) {
int temp = b;
b = a%b;
a = temp;
}

return a;
}

/* reduce z to lowest terms */
struct frac reduce(struct frac x)
{
struct frac z;

int c = gcd(x.numer, x.denom);
z.numer = x.numer/c;
z.denom = x.denom/c;

return z;
}

struct frac init(int a, int b)
{
struct frac z;

if (b < 0) { /* put sign in the numerator */
a = -a;
b = -b;
}

z.numer = a;
z.denom = b;
z = reduce(z);

return z;
}

int main(void)
{
int num, den;
struct frac z;
int c = 1;
char str[50];

printf("Input fraction (num/den): ");
scanf("%s", str);

scanf("%d%d", &num, &den);

if((num==0) && (den!=0))
{
if(num>=0){
num = -1*num;
}
printf("-%d/%d", num,den);
printf(" = -%d/%d", num,c);
return 0;
}

if (den==0)
{
if(num>0){
num = -1*num;
printf("%d/%d", num,den);
}
else if (num==0){
printf("-%d/%d", num,den);
}
printf("Floating exception");
return 0;
}

printf("%d/%d", num,den);

if ((den!=0) && (num!=0))
{
z = init(num,den);
printf(" = %d/%d", z.numer,z.denom);
}

return 0;
}

Example:

Input is: -5/-10

should return: 1/2

forked child process not terminating.

shrikanth — Sun, 03 Oct 2010 09:22:04 GMT

Hi,
I'm new to Linux,.

Here is the problem,,
I'm trying out some c programs, i have problem when i fork a child process,,its not terminating , i,e program is entering into an infinite loop.. even ctr+c not working..
what wrong am I doing..?
please replay early..
thank you..

Do you know any GPL project written in C?

misfi — Sun, 24 May 2009 04:20:39 GMT

Do you know any GPL project written in C?