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<stdio.h> snprintf family of functions in C99
Using the sprintf family of functions found in the C90 standard header <stdio.h> can be dangerous.
In the statement:
sprintf(buffer, "Error %d: Cannot open file '%s'", errno, filename);
the full output of the formatting operation is written into buffer regardless of whether there is enough space to hold it.
Consequently, more characters can be output than might fit in the memory allocated to the
string.
The snprintf functions found in the C99
version of <stdio.h> are safe versions of the sprintf functions that prevent buffer overrun. In the
statement:
snprintf(buffer, size, "Error %d: Cannot open file '%s'", errno, filename);
the variable size specifies the maximum
number of characters that can be written to buffer. The
buffer can never be overrun, provided its size is always greater than the size specified by
size.
Note The C standard does not define what should happen if
buffer + size exceeds 4GB (the limit of the 32-bit address
space). In this scenario, the ARM implementation of snprintf does not write any data to the buffer (to prevent wrapping the buffer
around the address space) and returns the number of bytes that would have been
written.