Can an invalid pointer clobber the new operator?

I have a problem with my code where it chokes on a "new" statement. This is what it looks like:

void String::set(char *cString)
{
/* This is a function in my own String class which is an
assignment of the c-style string pointed to by cString
to the String object. */

if(str != NULL)
delete[] str; // str is of type char*

int len = strlen(cString);
len++;
logfile << "about to allocate memory" << endl;
str = new char[len];
logfile << "memory allocated" << endl;
strcpy(str, cString);
}

This has been working fine for months, but all of sudden I am getting a run-time error in the program at the same point every time I run it. I have not modified the String class for months. The program successfully calls this function about a hundred times before it reaches the point where it fails. On checking the log file, I find that the "about to allocate memory" message appears, but the "memory allocated" message is not reached.

I can't see how a call to "new char[n]" can suddenly fail. I'm guessing that an invalid pointer somewhere else in the program is responsible for this. Can an invalid pointer actually reach and screw up the instructions of an operator? If not, any other ideas? It's a relatively small program, and the program fails at the same point if I cut the data by a third , so I'm sure it's not a case of running out of memory. I am using DJGPP.

Thanks in advance,
Sean

you can see whether its an out of memory problem by enclosing the call to new in a try/catch block. new throws std::bad_alloc when it cannot find the memory......

i.e.

try
{
char* pDynamic=new char[1000];
}
catch (std::bad_alloc&)
{
cerr<<"new failed to find memory";
exit(0);
}

You can delete pointers to NULL so
instead of

Code:

---

if(str != NULL)
    delete[] str; // str is of type char*

---

do this

Code:

---

delete[] str;

---

cString might be invalid but I can't be too sure.
That would throw of new for sure you might
want to throw in a assert statement such as

Code:

---

assert(len >= 0 && len < 100);

---

I hope you know how to use gdb because this
bug might require it.

Code:

---

str = new char[len];

---

str is global are you sure you release it, it might be
easier to manage the memory if you do something like this

Code:

---

char* upstring(char* s)
{
        char* p = NULL;
 
        if (s != NULL) {
                int n = strlen(s);
                p = new [n + 1];
                strcpy(p, s);
        }
        return p;
}

---

Then the class or function that owns str can handle
it locally. Another way could be just to use c++'s string's class

>>> new throws std::bad_alloc when it cannot find the memory......

To be ANSI compliant, it should, but many compilers including MS VC++ do not. They return NULL, (as they should with the new(nothrow) construction).