Dereferencing type-punned pointer will break strict-aliasing rules

Question

I used the following piece of code to read data from files as part of a larger program.

double data_read(FILE *stream,int code) {
        char data[8];
              


        

Answer 1

This doc summarizes the situation: http://dbp-consulting.com/tutorials/StrictAliasing.html

There are several different solutions there, but the most portable/safe one is to use memcpy(). (The function calls may be optimized out, so it's not as inefficient as it appears.) For example, replace this:

return *(short*)data;

With this:

short temp;
memcpy(&temp, data, sizeof(temp));
return temp;