Mohammed Salah's Blog

strlen() vs. sizeof() tip

Mohammed Salah — Sun, 26 Apr 2009 10:35:35 +0000

Only use sizeof() for locally allocated buffers.
Always use strlen() for variables passed from outside.

Why: using sizeof() with a pointer to char passed to you will return
the size of the pointer itself (which is 4 always) not the size of the
allocated space to that buffer.

Careful when using strncpy

Mohammed Salah — Sun, 26 Apr 2009 10:11:41 +0000

Copy characters from string

Copies the first num characters of source to destination. If the end of the source C string (which is signaled by a null-character) is found before num characters have been copied, destination is padded with zeros until a total of num characters have been written to it.

No null-character is implicitly appended to the end of destination, so destination will only be null-terminated if the length of the C string in source is less than num.
Parameters

destination
Pointer to the destination array where the content is to be copied.
source
C string to be copied.
num
Maximum number of characters to be copied from source.

Return Value
destination is returned.

C/C++ const trick

Mohammed Salah — Thu, 23 Apr 2009 15:05:09 +0000

int x = 7;

Now, what is the difference between each one of the next statements?

int *p = &x; // “p” is a modifiable pointer to a modifiable int

const int *p = &x; // “p” is a modifiable pointer to a read only int

int const *p = &x; // “p” is a read-only pointer to a modifiable int

const int const *p = &x; // “p” is a read-only pointer to a read-only int