Why do I get NZEC error here?

Question

My code here-

     void input(char* m)
{
    char ch;
    do
    {
        ch=getchar();
    }
    while(ch=='\n');
    int i=0;
    while(ch!='\n')
    {
        m[i++]=ch;
        ch=getchar();
    }
}

gives NZEC error. However, if I limit the input with a character count len , such as this-

void input(char* m, int len)
{
    char ch;
    do
    {
        ch=getchar();
    }
    while(ch=='\n');
    int i=0;
    while(ch!='\n'&&i<len-1)
    {
        m[i++]=ch;
        ch=getchar();
    }
}

it passes along fine. Why is that?

Answer 1

In the first case you have a buffer overflow !

Your while(ch!='\\n') will loop until a '\\n' regardless of the number of chars typed in. If more chars are typed than there is space in the char buffer pointed to by m , you might corrupt memory. Of course, in the second case, len will avoid this.

Please note that in both cases, you do not ensure a null terminator to your buffer. So if you process youd m as c-string you might also get not enough memory or a bufer overflow, as the string could be extremely long.

Have you ever considered defining your function as:

void input(std::string& m) {
    // ...
    m.push_back(ch); // instead of m[i++]=ch 
    // ...  
}