access violation with strcat() and strncat

**code987** · 01-22-2003

Why on earth am I getting access violations from the following two prorams, the first is using strcat(), and the last one is using strncat()....

// code
#include <iostream.h>
#include <string.h>

int main()
{
char *FName = "John";
char *LName = "Doe";

strcat(FName, LName);

cout << FName << endl;

return 0;
}

// code

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

int main()
{
char *FName = "John";
char *LName = "Doe";

strncat(FName, LName, 3); // will only print the first 3 char's

cout << " " << FName << endl;

return 0;
}

any ideas?

**Polymorphic OOP** · 01-22-2003

Because you aren't allocating enough memory to hold the bigger string.

Code:

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

int main()
{
    char FName[8] = "John";
    char *LName = "Doe"; 

    strcat(FName, LName);
    cout << FName << endl;

    return 0;
}

**code987** · 01-22-2003

my bad, thanks

**Hammer** · 01-22-2003

>>Because you aren't allocating enough memory to hold the bigger string.
You mean no memory. This:
>char *FName = "John";
is not safe to modify as its a pointer to data that could be in read only memory. You need to use an array, like Poly showed.

**Polymorphic OOP** · 01-22-2003

Yeah, I think they should make it a syntax error when you do that.

It should only be valid to do something like:

const char* String = "Blah";

That would make a lot more sense

**grib** · 01-22-2003

It should only be valid to do something like:
const char* String = "Blah";

This would make a great deal of sense, but it would break Soooooo much code.
It's even more fun because when the compiler lays out space for the string litterals it likes to stick them just before all the sensitive fiddily bits.

**Polymorphic OOP** · 01-22-2003

Originally posted by grib
This would make a great deal of sense, but it would break Soooooo much code.

Yeah, it should've been like that from the start. Doesn't make any sense why it wasn't. Too late now, unfortunately.

**Eibro** · 01-22-2003

Embrace C++!

Code:

#include <string>

// ...

using std::string;
string fname = "John";
fname += "Doe";

Now you don't have to worry about any of that bullcock.

**Polymorphic OOP** · 01-22-2003

There's no fun in that!

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