byte array to double

I have a four byte char array and I w开发者_StackOverflowant to convert it to double. How can I achieve this in C.

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float and double are so closely related in C that an explicit conversion is probably not needed. However, it would be necessary for transmission to another system, or to match a data format specification. This will do what you ask:

union {
    char   c [4];
    float  f;
} x;
double d;

memcpy (x.c, character_source, sizeof x.c);
d = x.f;