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Hi.. I need to use the cos and sin functions. what are the libraries I need to add ? is it only <math.h> ? if yes, i tried that and i got error message:
/cygdrive/h/Ex3/FFT/FFT.c(45): error: undefined reference to 'cos'
Thankx
The error you got was "undefined reference". That's a linker error message, telling you that it found no implementation of cos() in any of the places you told it to look. I.e. the problem is not that the code calls cos() in some strange way --- it's that it calls it at all, and that the linker can't find the actual function.
Time to open the documentation and find the library reference manual, to see where the implementation of cos() is supposed to be.
At the same time, have a closer look at the definition of PI:
float PI=3.147;
Yes it is 3.14159 .
How can i define this floating value as a preprocessor in a rational fromat 22/7:
#define PI (22/7)f ? or (22.0f/7.0f) ? or how ?
The compiler will convert (22./7.) into 3.1428...
If you want to use PI somewhere (named M_PI in the standard library) then it is best to define it as M_PI 3.14159265358979323846 (use whatever precision you need, and the target supports).
It is only if you play with fixed-point arithmetic that it may be meaningful to play with the rational format. In that case you can decide if you want to define PI as a fixed-point value, or if you want to separate the multiplication and the division, possibly gaining you extra precision if you manually keep track of overflow and number of digits in intermediate results.
Actually i cant find the M_PI .. where is it ? in which library? is it in <math.h> ?? Note: i am using GNU compiler version 4.1.1
The nice little tool "grep" will tell you which file it is in. If grep can't find the symbol in any of your existing include files, then it just isn't there. Embedded compilers doesn't have all standard symbols defined...
i forgot to ask,, the angle of a cos or sin function is in radians or degrees.??
There are a huge number of functions available in the standard library. Hence, the only reasonable way you can make use of them is by making it a habit to check the manual. It will - of course - describe the parameters for the available functions.