problem getting function to change value of array element

[hansfordmc]

Newbie to C++ programming. I am trying to pass a pointer to an array element to a function and have the function change the value, but I'm getting a memory overwrite error when the program runs. The program sends a string to the function which is then suppose to change all of the letters to uppercase. Any help would be appreciated.

#include "stdafx.h"
#include <iostream>
#include <string>

using namespace std;
using namespace System;

void toUpper(char* letter, int len){
	
	char lower_case[] = { "abcdefghijklmnopqrstuvwxyz" };
	char upper_case[] = { "ABCDEFGHIJKLMNOPQRSTUVWXYZ" };
	int array_size = 1 * sizeof(lower_case);
	int count = 0;

		while(count < len){
			
			if(*letter == ' ') {
				count++;
				letter++;
				continue;
			}
			
			for(int i = 0; i < array_size; i++){

				if(*letter == lower_case[i]) {
					*letter = upper_case[i];
					break;
				}
				else if(*letter == upper_case[i]){
						*letter = upper_case[i];
						break;
				}
			}
		letter++;
		count++;
		}
}
	

int main(array<System::String ^> ^args)
{
	char* stars[][80] = { "Robert Redford", "Chuck Norris", "Alec Baldwin" };
	int count = 0;
	int len = strlen(*stars[0]);
	toUpper(*stars[0], len);
	cout << *stars[0] << endl;
}

|

[bhushan1980]

Hi,
If in case you want toupper() function provided by STL? Here is one of the references:

http://www.cplusplus.com/reference/c...ctype/toupper/

you can find many more if only you google

I have modified your code as under:

#include "stdafx.h"
#include <iostream>
#include <string>
#include <ctype>

using namespace std;
// using namespace System;   I hope you are not using managed C++ and if so use that forum

size_t getPtrSize( char *ptr )
{   return sizeof( ptr );  }

void toUpper(char* letter, int len)
{
	char lower_case[] = { "abcdefghijklmnopqrstuvwxyz" };
	char upper_case[] = { "ABCDEFGHIJKLMNOPQRSTUVWXYZ" };

	// commented out .... int array_size = 1 * sizeof(lower_case);
                // MSDN says that when sizeof operates on char type data the result is always 1
                // This indicates that your method reads only first char in your array
                // Also, it seems, sizeof accepts a pointer argument and you are passing static array
                
                int array_size = static_cast<int>getPtrSize(lower_case)
	int count = 0;
	while(count < len)
               {
	    if(*letter == ' ')
                   {
	       count++;
	       letter++;
	       continue;
	   }
  	   for(int i = 0; i < array_size; i++)        // you can directly call getPtrSize here...
                   {
                       if(*letter == lower_case[i])
                       {
	            *letter = upper_case[i];
	             break;
                       }
	       else if(*letter == upper_case[i])
                              {
		   *letter = upper_case[i];
		   break;
	              }
	  }
	  letter++;
	  count++;
            }
}

// the following main you are using is for managed C++....and this is not the right forum
// int main(array<System::String ^> ^args)
// the main in standard C++ is as under...
// int main(int argc, char **argv)...
// However, you are not inputing anything from commandline
// You are setting the string values from within the program and so u can use the following
int main(void)
{
	char* stars[][80] = { "Robert Redford", "Chuck Norris", "Alec Baldwin" };
	int count = 0;
	int len = strlen(*stars[0]);
	toUpper(*stars[0], len);
	cout << *stars[0] << endl;
}
|

I have just about hinted you. The code should now work barring a few compile errors. Those would not be difficult to detect.

Regards,
Bhushan

[CoolPG]

You are trying to change the value of a const char* type which is not allowed and the operation fails with a access violation error.

You should try something like this :

void main(void)
{

char* myTest = (char*)malloc( sizeof("Robert Redford") );

strcpy( myTest, "Robert Redford" );
int count = 0;
int len = strlen(myTest);
toUpper(myTest, len);
std::cout << myTest << endl;

free( myTest);
system("pause");
}

I had discarded your function part... Now it will work.

Also do a brushup on your basics in pointer by refering a book.. good luck

[Paul McKenzie]

Newbie to C++ programming.

int main(array<System::String ^> ^args)

You are not learning "true" C++, as that line of code is not C++. It is an extension of the C++ language that Microsoft calls "Managed C++", and is not proper C++. That code isn't even relevant to this forum (there is a separate forum called Managed C++).

Secondly, there is already a toupper() and tolower() functions in the C++ library. If you want to turn a non-const sequence of characters to upper or lower case, use std::transform().

#include <algorithm>
#include <cctype>
#include <string>
#include <iostream>

using namespace std;

int main()
{
    string s1 = "This is a test";
    transform(s1.begin(), s1.end(), s1.begin(),  toupper);  // convert to upper case
    cout << s1;  
}

Third, any beginner C++ program using "strlen", "strcpy", etc. IMO is flawed. No beginner C++ program should be using these functions, instead the usage of std::string class should replace these calls.

Regards,

Paul McKenzie

[Paul McKenzie]

You should try something like this :

void main(void)

The main() function returns int, not void.

char* myTest = (char*)malloc( sizeof("Robert Redford") );

Why introduce malloc() and free()? The code below does the same thing:

char myTest[sizeof("Robert Redford")] = "Robert Redford";

Regards,

Paul McKenzie

[CoolPG]

Thanks for pointing out mistakes, Paul

I'm sorry i got result what the OP is asking for. I didnt know that this was a risky method.

And, about the main() i strongly believe i had seen somewhere in a Microsoft page where they says main can return void type also.

and, if i'm compiling a program in MSVC with void main() no compiler errors or warnings are thrown out. The standard(as per C99) suggests main should return int.

But i'm confused with the Microsoft statement and C99 standard suggestion.

Here is the MSDN link i had.

http://msdn.microsoft.com/en-us/libr...wh(VS.80).aspx

[Paul McKenzie]

Thanks for pointing out mistakes, Paul

I'm sorry i got result what the OP is asking for. I didnt know that this was a risky method.

And, about the main() i strongly believe i had seen somewhere in a Microsoft page where they says main can return void type also.

It doesn't matter what Microsoft says. The ANSI/ISO C++ specification states that the main() function returns an int.

http://www.parashift.com/c++-faq-lit....html#faq-29.3

Secondly, you aren't really "voiding" anything by making main() "void". The main() function still returns an int to the system. Look at the runtime when main() terminates -- an int is returned.

Regards,

Paul McKenzie

[Lindley]

Microsoft throws a lot of non-standard extensions into their compiler. Doesn't mean it's always a good idea to use them.

[CoolPG]

Thanks Paul and Lindley.

1 more doubt.

Secondly, you aren't really "voiding" anything by making main() "void". The main() function still returns an int to the system. Look at the runtime when main() terminates -- an int is returned.

So, if it is the case why ISO is restricting programmers from using "void" as return type for main() and is there any underlying risk in using this void type. sorry for annoying, i'm a beginner.




PS : Dont consider this as trolling or thread hijacking. but this doubt is quite situational, and i dont believe in need of another thread for asking this.

[laserlight]

So, if it is the case why ISO is restricting programmers from using "void" as return type for main()

Because it was chosen to standardise on int as the return type for the global main function, at least for programs in a hosted environment.

and is there any underlying risk in using this void type.

In generaly, the return type depends on the function. If you are talking about the risk of using void as the return type of the global main function, then there is the risk that your otherwise perfectly portable program may fail to compile on another compiler that reasonably conforms to the C++ standard.

[CoolPG]

Thank you laserlight for replying and clearing the doubt.

It was disappointing when other people went away not replying after getting their repute

[Paul McKenzie]

So, if it is the case why ISO is restricting programmers from using "void" as return type for main() and is there any underlying risk in using this void type. sorry for annoying, i'm a beginner.

Since C++ borrows a lot of the ISO standard from 'C', some C compilers will not flag the "void main()" as an error, but will produce unpredictable results when the program is run.

There was a link to an article (don't remember the link now) where it was shown that for some environments "void main()" produced a crash when the program terminated due to the return not generating the correct code.

For 'C', you can make any function return a different type than what it actually does return. Of course, doing so produces unpredictable results, and I guess "void main()" can fall into this category.

Edit:

Here is the link:

http://users.aber.ac.uk/auj/voidmain.shtml

Regards,

Paul McKenzie