[SOLVED] int main(int argc, char **argv[]) having trouble getting value out of array argv[ ] C programming.

BW-userx · 04-12-2017, 12:23 PM

this may to some seem like a stupid question to them that already know how to do this, But this is using pointers so I have no idea how to completely deal with them.

Getting the number off of the command line that is seen as a string? example

Code:

programName 3

get what number was typed in CLI for processing.
break it down? .. OK

If I run just this function I get the results I need to show me my logic in correct.

Code:

#include <stdio.h>

int main(int argc, char **argv[])
{
    int i = 1; 
    // zero based array 
    // then look for greater then zero 
    // zero being the program name

    if ( argc >= 1 )
      printf("argc %d argv[argc-1] %s\n", argc, argv[argc-1]);
   
     /*
     if (argc >= 1 )
     {
       i=argv[argc-1];
	printf("this is i %d\n", i);
      }
      **/
}

results

Code:

userx@slackwhere⚡~/bin/C-files $./a.out 5                                                            
argc 2 argv[argc-1] 5

That work. It is when I umcomment out the next block of code to get the value out of the element in argv[argc-1] and try to assinge it to 'i'

is where i get a cast issue.

Code:

userx@slackwhere⚡~/bin/C-files $gcc Yathee.c
Yathee.c: In function 'main':
Yathee.c:29:9: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
        i=argv[argc-1];

but when I type set it that too does not work.

Code:

userx@slackwhere⚡~/bin/C-files $gcc Yathee.c
Yathee.c: In function 'main':
Yathee.c:28:11: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
         i=(int)argv[argc];

nor this

Code:

  if (argc >= 1 )
     {
       i=&argv[argc-1];
	printf("this is i %d\n", i); 
      }

which I got off somewhere else from the same error message googled.
nor this

Code:

userx@slackwhere⚡~/bin/C-files $gcc Yathee.c
Yathee.c: In function 'main':
Yathee.c:28:11: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
         i=(int16_t)argv[argc];

int16_t because It just popped up in Kwrite as a selection, so why not try that too?

I have already googled the this error and what I tried on what I found still did not work.

Quote:

assignment makes integer from pointer without a cast [-Wint-conversion]

Anyways regardless, can someone show me how to get the value out of a pointer( I think is a char) and cast it to int properly?

as I keep getting the same error regardless of what I do.

rknichols · 04-12-2017, 12:33 PM

Quote:

Originally Posted by BW-userx

Code:

#include <stdio.h>

int main(int argc, char **argv[])
{

That should be either of these:

Code:

int main(int argc, char *argv[])
/*   OR   */
int main(int argc, char **argv)

I find the first declaration ("an array of pointers") more intuitive, but the two are equivalent.

Then your 'printf("argc %d argv[argc-1] %s\n", argc, argv[argc-1])' should work;

BW-userx · 04-12-2017, 12:53 PM

Quote:

Originally Posted by rknichols

That should be either of these:

Code:

int main(int argc, char *argv[])
/*   OR   */
int main(int argc, char **argv)

I find the first declaration ("an array of pointers") more intuitive, but the two are equivalent.

Then your 'printf("argc %d argv[argc-1] %s\n", argc, argv[argc-1])' should work;

ha ha mixing the chili soup with sweet apples just does not taste as good. thanks!

let me put them two to the test.

first
int main(int argc, char **argv)

Code:

#include <stdio.h>

int main(int argc, char **argv)
{
  
  
  int i =1; 
  
   
     if ( argc >= 1 )
      printf("argc %d argv[argc-1] %s\n", argc, argv[argc-1]);
   
     
     if (argc >= 1 )
     {
       i = argv[argc-1];
       printf("this is i %d in argv[argc-1] %s\n", i ,  argv[argc-1]);
      }
      
return 0;
}

results:

Code:

userx@slackwhere⚡~/bin/C-files $gcc array.c
array.c: In function 'main':
array.c:22:10: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
        i = argv[argc-1];

next
int main(int argc, char *argv[])

Code:

#include <stdio.h>

int main(int argc, char *argv[])
{
  
  
  int i =1; 
  
   
     if ( argc >= 1 )
      printf("argc %d argv[argc-1] %s\n", argc, argv[argc-1]);
   
     
     if (argc >= 1 )
     {
       i = argv[argc-1];
	printf("this is i %d in argv[argc-1] %s\n", i ,  argv[argc-1]);
      }
      
return 0;
}

results:

Code:

userx@slackwhere⚡~/bin/C-files $gcc array.c
array.c: In function 'main':
array.c:22:10: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
        i = argv[argc-1];
          ^

Looks like a fail on both accounts to me.

I think you may have missed something.

"Anyways regardless, can someone show me how to get the value out of a pointer( I think is a char) and cast it to int properly?"

smallpond · 04-12-2017, 12:56 PM

You can't cast a string to an int. You need to do the conversion by calling a function like atoi.

BW-userx · 04-12-2017, 01:33 PM

Quote:

Originally Posted by smallpond

You can't cast a string to an int. You need to do the conversion by calling a function like atoi.

StrToInt what was I thinking... prob wasn't ... thanks.... points given.

BW-userx · 04-12-2017, 02:01 PM

Answer:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char *argv[])
{
  
  
  int i =1; 
  char num[7];
  
     if ( argc >= 1 )
      printf("argc %d argv[argc-1] %s\n", argc, argv[argc-1]);
     
   
     
     if (argc >= 1 )
     {
       strcpy(num, argv[argc-1]);
       i = atoi(num);
	printf("this is i %d in argv[argc-1]%s\n", i ,  argv[argc-1]);
      }
      
return 0;
}

or a direct call without copying string first.

Code:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
  
  
  int i =1; 
  
  
     if ( argc >= 1 )
      printf("argc %d argv[argc-1] %s\n", argc, argv[argc-1]);
     
   
     
     if (argc >= 1 )
      
       i = atoi(argv[argc-1]);
	printf("this is i %d in argv[argc-1]%s\n", i ,  argv[argc-1]);
      }
      
return 0;
}

rknichols · 04-12-2017, 04:09 PM

Quote:

Originally Posted by BW-userx

int main(int argc, char *argv[])

Code:

#include <stdio.h>

int main(int argc, char *argv[])
{
  
  
  int i =1; 
  
   
     if ( argc >= 1 )
      printf("argc %d argv[argc-1] %s\n", argc, argv[argc-1]);
   
     
     if (argc >= 1 )
     {
       i = argv[argc-1];
	printf("this is i %d in argv[argc-1] %s\n", i ,  argv[argc-1]);
      }
      
return 0;
}

results:

Code:

userx@slackwhere⚡~/bin/C-files $gcc array.c
array.c: In function 'main':
array.c:22:10: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
        i = argv[argc-1];
          ^

Looks like a fail on both accounts to me.

That second "if ..." block was commented out in your original code, so I didn't examine it. What are you trying to assign to "i"? If it's the value of the pointer (i.e., an address in virtual memory), then you just need to do an explicit cast:

Code:

i = (int)argv[argc-1]

That's going to have portability problems on a 32-bit machine where sizeof(int) < sizeof(char *), but it will demonstrate the principle just fine on a 64-bit machine.

If the actual argument passed to the program is a numeric string and you want its value, then you need to use atoi(), as others have suggested.

BW-userx · 04-12-2017, 04:18 PM

Quote:

Originally Posted by rknichols

That second "if ..." block was commented out in your original code, so I didn't examine it. What are you trying to assign to "i"? If it's the value of the pointer (i.e., an address in virtual memory), then you just need to do an explicit cast:

Code:

i = (int)argv[argc-1]

That's going to have portability problems on a 32-bit machine where sizeof(int) < sizeof(char *), but it will demonstrate the principle just fine on a 64-bit machine.

If the actual argument passed to the program is a numeric string and you want its value, then you need to use atoi(), as others have suggested.

and that is what I did, but error checking to insure it is a "char" number 1-6 and not a char a-z [anything else] .. will be later on.

and as far as not inspecting that block of commented out code,
It's all cool dude, you must have just missed this is all no big deal, drinks on me..

Code:

That work[s]. It is when I umcomment out the next block of code to get the
value out of the element in argv[argc-1] and try to assinge it to 'i'

is where i get a cast issue.

Laserbeak · 04-18-2017, 10:40 PM

Hopefully this helps:

Code:

| => cat argtest.c
#include <stdio.h>
#include <stdlib.h>

int main (int argc, char *argv[]) {

	for (int i = 0; i < argc; i++) {
		printf ("Argument: %d Value:%s\n", i, argv[i]);
	}
        exit (0);
}

| => clang -o argtest argtest.c
| =>

test output:

Code:

| => ./argtest 0 1 223 helloWorld! MacOS X
Argument: 0 Value:./argtest
Argument: 1 Value:0
Argument: 2 Value:1
Argument: 3 Value:223
Argument: 4 Value:helloWorld!
Argument: 5 Value:MacOS
Argument: 6 Value:X
| =>

BW-userx · 04-19-2017, 09:00 AM

Quote:

Originally Posted by Laserbeak

Hopefully this helps:
[/code]

test output:

Code:

| => ./argtest 0 1 223 helloWorld! MacOS X
Argument: 0 Value:./argtest
Argument: 1 Value:0
Argument: 2 Value:1
Argument: 3 Value:223
Argument: 4 Value:helloWorld!
Argument: 5 Value:MacOS
Argument: 6 Value:X
| =>

Hey thanks, now I am working on

get input
process
store results
show results
ask for more input
wait for input
repeat

Loop

Thanks

Laserbeak · 04-23-2017, 01:31 AM

Quote:

Originally Posted by BW-userx

Hey thanks, now I am working on

get input
process
store results
show results
ask for more input
wait for input
repeat

Loop

Thanks

This should help, but it's not particularly safe and I'll leave the storage part up to you

Code:

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>

char *processInput (char *inValue);

int main (int argc, char *argv[]) {
    while (1) {
        printf("Please enter a string [max 1000 chars] (press return to quit): ");
        char *input = (char *)malloc(1001);
        gets(input);
        if (strlen(input) == 0)
            break;
        char *theOutValue = processInput (input);
        printf("%s\n", theOutValue);
        free (input);
        free (theOutValue);
 
    }
    return (0);
}

char *processInput (char *inValue) {
    
    //process by making all caps
    
    char *outValue =  (char *)malloc(sizeof(inValue));
    for (int i = 0; (outValue[i] = toupper(inValue[i])); i++);
    return outValue;
}

BW-userx · 04-23-2017, 02:11 PM

Quote:

Originally Posted by Laserbeak

This should help, but it's not particularly safe and I'll leave the storage part up to you

Code:

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>

char *processInput (char *inValue);

int main (int argc, char *argv[]) {
    while (1) {
        printf("Please enter a string [max 1000 chars] (press return to quit): ");
        char *input = (char *)malloc(1001);
        gets(input);
        if (strlen(input) == 0)
            break;
        char *theOutValue = processInput (input);
        printf("%s\n", theOutValue);
        free (input);
        free (theOutValue);
 
    }
    return (0);
}

char *processInput (char *inValue) {
    
    //process by making all caps
    
    char *outValue =  (char *)malloc(sizeof(inValue));
    for (int i = 0; (outValue[i] = toupper(inValue[i])); i++);
    return outValue;
}

Interesting. Thanks --
the storage shouldn't be too much of an issues if any. it is all of that formatting the output to screen I got a do.

BW-userx · 04-23-2017, 02:21 PM

@Laserbeak

just a quick Q: out of curiosity

why is it telling me this?

Code:

userx%slackwhere ⚡ C-files ⚡> gcc malchar.c
malchar.c: In function ‘main’:
malchar.c:12:9: warning: implicit declaration of function ‘gets’ [-Wimplicit-function-declaration]
         gets(input);
         ^
/tmp/ccFJrg4n.o: In function `main':
malchar.c:(.text+0x39): warning: the `gets' function is dangerous and should not be used.

Laserbeak · 04-23-2017, 02:40 PM

Quote:

Originally Posted by BW-userx

@Laserbeak

just a quick Q: out of curiosity

why is it telling me this?

Code:

userx%slackwhere ⚡ C-files ⚡> gcc malchar.c
malchar.c: In function ‘main’:
malchar.c:12:9: warning: implicit declaration of function ‘gets’ [-Wimplicit-function-declaration]
         gets(input);
         ^
/tmp/ccFJrg4n.o: In function `main':
malchar.c:(.text+0x39): warning: the `gets' function is dangerous and should not be used.

I'm not sure why you're getting the "implicit declaration" message, as long as you #include <stdio.h>. The not safe warning is because gets() doesn't do any error checking as far as the length of the string inputed and the size of string allocated to store it, so it can overrun the buffer, leading to either a crash or worse inserting malicious code into your program.

My compiler simply says "warning: this program uses gets(), which is unsafe."

NevemTeve · 04-24-2017, 03:58 AM

Function 'gets' mustnot be used. Since around 1970. I was two year old then, now I am 49.