Problem passing a ptr to a fxn into a fxn

This is a discussion on Problem passing a ptr to a fxn into a fxn within the C Programming forums, part of the General Programming Boards category; I am using the wavelet code from numerical recipes in C. http://www.library.cornell.edu/nr/bookcpdf/c13-10.pdf When I try to call a function that ...

  1. #1
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    Problem passing a ptr to a fxn into a fxn

    I am using the wavelet code from numerical recipes in C.
    http://www.library.cornell.edu/nr/bookcpdf/c13-10.pdf
    When I try to call a function that calls another function I get the following error in MS Visual C++:

    wavelet.obj : error LNK2001: unresolved external symbol "void __cdecl wt1(float *,unsigned long,int,void (__cdecl*)(float *,unsigned long,int))" (?wt1@@YAXPAMKHP6AX0KH@Z@Z)
    Debug/w3.exe : fatal error LNK1120: 1 unresolved externals
    Error executing link.exe.


    The relevant code is as follows:

    void daub4(float *, unsigned long, int);
    void wt1(float *, unsigned long, int, void (*)(float [], unsigned long, int));

    void main(){
    ...
    wt1(x, numPoints-1, 1, daub4);
    ...
    }

    void wt1(float a[], unsigned long n, int isign,
    float(*wtstep)(float [], unsigned long, int)){
    //One-dimensional discrete wavelet transform. This routine implements the pyramid algorithm,
    //replacing a[1..n] by its wavelet transform (for isign=1), or performing the inverse operation
    //(for isign=-1)
    //. Note that n MUST be an integer power of 2. The routine wtstep, whose
    //actual name must be supplied in calling this routine, is the underlying wavelet .lter. Examples
    //of wtstep are daub4 and (preceded by pwtset) pwt.
    unsigned long nn;

    if (n < 4) return;
    if (isign >= 0) { //Wavelet transform.
    for (nn=n;nn>=4;nn>>=1) (*wtstep)(a,nn,isign);
    //Start at largest hierarchy, and work towards smallest.
    } else { //Inverse wavelet transform.
    for (nn=4;nn<=n;nn<<=1) (*wtstep)(a,nn,isign);
    //Start at smallest hierarchy, and work towards largest.
    }
    }

    void daub4(float *a, unsigned long n, int isign){
    .......
    .......
    }


    Please help me to pass daub4 into wt1!

    Thanks,
    *Bob_ptr

  2. #2
    Just Lurking Dave_Sinkula's Avatar
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    Code:
    void wt1(float *, unsigned long, int, void (*)(float [], unsigned long, int));
    Code:
    void wt1(float a[], unsigned long n, int isign,
             float(*wtstep)(float [], unsigned long, int)) {
    Make the declaration match the definition.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  3. #3
    Code Goddess Prelude's Avatar
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    Code tags will make your declaration/definition mismatch problems easier to find. And for those of us that still eyeball the unformatted code, we rarely miss this:
    Code:
    void main(){
    main returns int for the majority of software. If you're giving us code from a freestanding environment then mention it so that we don't jump all over you. Otherwise, you're wrong and we're right.
    My best code is written with the delete key.

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