Thread: Segmentation fault (core dumped)

This is doing my head in and I have been at it for hours. I have googled with no luck. tried different loops again no joy.

I have done what I need to do however without using an array, its messy and its limited, now I am improving my code by using an array.

The code is meant to assign the first character after a space to an array. The program runs fine providing there are no spaces.. HA. If there is a space I get "Segmentation fault (core dumped)

So in turn given I get the above error when I input a space I am 99% sure the problem is in the code below. But I can not figure it out.

I will post the whole code if required but I didn't want to waste anyones time.

Code:

    
for (int i = 0; i < strlen(input); i++)    {
        if (input[i] == 32)    // Checking if a space is present.
        {
            count++;   // Counting spaces from input to use later.
            *argv[x] = input[i + 1];   // assigning the char after space to an array.
            x++;        
            argc++;
        }
    }

Thanks in advance.

Code:

*argv[x] = input[i + 1];

Am i wrong assuming I can use x to place the character in that position of the array?
x is declared earlier in the program and as you can see it increases by one if that if statement is initialised in the event another space or '32' is present.

Also I am not sure why I cant use this:

Code:

 argc++;

Thanks, Ryan

I should add I am trying to use an unassigned array and it will only increase as required using the above code appose to using a loop to detect how many places I need to allocate the array... Essentially I am attempting to eliminate lines of code, more so for learning purposes seeing if I can take a different approach (taking less steps)

I don't think I've ever seen anyone attempt to use argv or argc in any other way that treats them as constants.

Originally Posted by Ryan Huddo

I should add I am trying to use an unassigned array and it will only increase as required using the above code appose to using a loop to detect how many places I need to allocate the array... Essentially I am attempting to eliminate lines of code, more so for learning purposes seeing if I can take a different approach (taking less steps)

You haven't told us what argv and argc are. The presumption is that these are the canonically-named parameters to main, but that doesn't make much sense the way you're using them. Post your entire program so we can see what's going on here.

@stahta01: It is legal to modify argc and even to modify the strings pointed to by argv (although you would obviously need to stay within the original lengths).

Please post the smallest complete code that illustrates your problem. The snippet you posted leaves too much to one's imagination. For example how and where were all those variables defined? While argv and argc are normally associated with command line arguments that is not always the case. Also even though the command line arguments are not constants, I recommend you consider them as constants anyway.

Jim

Originally Posted by laserlight

In that case, command line arguments do not come into play at all.


No, you cannot, at least not when they conventionally denote the number of command line arguments and the command line arguments themselves. But why would you need to do so? Since you are obtaining the input from the user (presumably) via standard input, you could just work with that.

Ah well that answers that issue, that brings me back to the first set of code i wrote, essentially:

Code:

// GetString
// for loop to find spaces
// - allocate spaces into an int
// use value to assign an array
// for loop to assign correct characters to the array as required.
// printf.

So is this the only way or can I assign a undeclared array and increase it as required during the only for loop, like I ATTEMPTED to do with the above.
e.g.

Code:

array[a]
// GetString
// for loop
// - Check spaces
// - assign char to array
// - array++
//printf.

Cheers, Ryan

Originally Posted by phantomotap

the expression `*argv[x] = input[i + 1]` writes to memory you don't own.
Soma

Ahhh, makes so much sense, haha learning curb.

Just letting everyone know I figured it out, I don't completely understand it and if someone wants to explain it to me please feel free, but working code as follows;

Code:

int main(void){
    string input;
    int count = 1;
    int x = 1;
    
    printf("Input ");
    input = GetString();
    
    int *init = malloc(strlen(input) * sizeof(*init));          //new line. 
    
    for (int i = 0; i < strlen(input); i++)
    {
        if (input[i] == 32)
        {
            count++;
            init[x] = input[i + 1];
            x++;
        }
    }
    free(init);
    init[0] = input[0];
    
    for (int i = 0; i < count; i++)
    {
        printf("%c\n", init[i]);
    }
}

Thanks everyone for there input

Ryan