[Solved] Function strnset() in C and how to use it

Question

You are either ignoring compiler warnings (don’t — the compiler doesn’t complain unless it spotted a bug in your code) or you aren’t compiling with enough warnings enabled (or, possibly, you are using an ancient and unhelpful C compiler).

The lines you ask about are basically the same:

strnset(str1, ("%s", str1[strlen(str1)-1]), 1);

The second argument to strnset() is ("%s", str1[strlen(str1)-1]), which is a comma-expression, and there is no side-effect in the LHS, so your compiler should be warning about something like that. A better, simpler way of writing that call would be:

strnset(str1, str1[strlen(str1)-1], 1);

That probably copies the last character of the string over the first character of the string. Certainly, str1[strlen(str1)-1] is the last character in the string. This is presumably somewhat similar to using either:

memset(str1, str1[strlen(str1)-1], 1);
str1[0] = str1[strlen(str1)-1];

The strnset() function is neither a part of the Standard C library nor a part of POSIX. IBM documents it, but the Linux manual pages don’t seem to do so. […time passes…] Ah, Microsoft documents strnset() and _strnset() as being Microsoft-specific.

Accepted Answer

You are either ignoring compiler warnings (don’t — the compiler doesn’t complain unless it spotted a bug in your code) or you aren’t compiling with enough warnings enabled (or, possibly, you are using an ancient and unhelpful C compiler).

The lines you ask about are basically the same:

strnset(str1, ("%s", str1[strlen(str1)-1]), 1);

The second argument to strnset() is ("%s", str1[strlen(str1)-1]), which is a comma-expression, and there is no side-effect in the LHS, so your compiler should be warning about something like that. A better, simpler way of writing that call would be:

strnset(str1, str1[strlen(str1)-1], 1);

That probably copies the last character of the string over the first character of the string. Certainly, str1[strlen(str1)-1] is the last character in the string. This is presumably somewhat similar to using either:

memset(str1, str1[strlen(str1)-1], 1);
str1[0] = str1[strlen(str1)-1];

The strnset() function is neither a part of the Standard C library nor a part of POSIX. IBM documents it, but the Linux manual pages don’t seem to do so. […time passes…] Ah, Microsoft documents strnset() and _strnset() as being Microsoft-specific.