unusual compiling problem

[iofthemourning]

I'm running Hardy Heron with gcc and build-essentials installed.

I have a C program that includes math.h at the beginning and uses the pow function. pow WORKS in the main function but if it is in any other function (absolutely any other), I get a really odd error message when I try to compile:


/tmp/ccxeWacg.o: In function 'det':
wah.c:(.text+0x46b): undefined reference to 'pow'
collect2: ld returned 1 exit status

What makes this especially frustrating and perplexing is that this code compiled and ran flawlessly on windows with Cygwin.

Has anybody experienced anything like this or know of a solution?

Thanks

-i

[samjh]

Do you mind posting the source so we can try to compile it ourselves?

It looks like a very strange problem.

[iofthemourning]

sure thing.the error comes up in the det function but if I comment out the line in det with pow, it compiles (note: pow is still in main).



#include <stdio.h>
#include <stdlib.h>
#include <math.h>



#define MATRIX_NOT_INITIALIZED "Matrix Not Initialized.\n"

#define DISPLAY_SEPARATOR "--------\n"

struct _matrix{

int rows;

int cols;

double* values;

};

typedef struct _matrix matrix;



typedef matrix *matrix_pointer;



matrix_pointer matrix_new(int rows, int columns, double *numbers) {

int i, j;

matrix_pointer new_matrix = (matrix_pointer) (malloc(sizeof(matrix)));



new_matrix->values = (double *)(malloc(rows*columns*(sizeof(double))));

new_matrix->rows=rows;

new_matrix->cols=columns;

for(i=0;i<rows;i++) {

for(j=0;j<columns;j++) {

new_matrix->values[(i*columns)+j]= numbers[(i*columns)+j];

}

}

return new_matrix;

}





void matrix_display(matrix_pointer matrix, int precision) {

int i,j;



printf("%s", DISPLAY_SEPARATOR);

for(i=0;i<matrix->rows;i++) {

for(j=0;j<matrix->cols;j++) {

if(j==matrix->cols-1) {

printf("%.*f\n", precision,matrix->values[(i*matrix->cols)+j]);

}

else {

printf("%.*f, ",precision, matrix->values[(i*matrix->cols)+j]);

}



}

}



}





void matrix_free(matrix_pointer matrix)

{

if (matrix==NULL)

printf(MATRIX_NOT_INITIALIZED);

if (matrix->values != NULL)

free(matrix->values);



free(matrix);

}



matrix_pointer matrix_shrink(matrix_pointer matrix, int row, int col){

int rows=matrix->rows-1;

int cols=matrix->cols-1;

matrix_pointer lawl;

double *nums=malloc(sizeof(double)*((rows)*(cols)));

int i, j, k=0;

for (i=0; i<matrix->rows; i++){

for (j=0; j<matrix->cols; j++){

if (i!=row && j!=col){

nums[k]=matrix->values[i*matrix->cols+j];

k++;

}

}

}

lawl=matrix_new(rows, cols, nums);

return lawl;

}



int det(matrix_pointer matrix){

int sum=0, i;

matrix_pointer temp;

if (matrix->rows==2 && matrix->cols==2){

return matrix->values[0]*matrix->values[3]-matrix->values[1]*matrix->values[2];

}

else{

for(i=0; i<matrix->rows;i++){

temp=matrix_shrink(matrix, 0, i);

sum+=(matrix->values[i])*pow(-1,i)*det(temp);

matrix_free(temp);

}

return sum;

}



}

void numbers_read(double *numbers, int length){

int x;

for (x=0; x<length; x++){

if(scanf("%lf", numbers++)!=1){

printf("error\n");

}

}

}



int main(void){
printf("%lf\n", pow(-4,2));
int i=3, j=3;

double *nums=malloc(sizeof(double)*i*j);

numbers_read(nums, i*j);

matrix_pointer blah=matrix_new(i, j, nums);

matrix_display(blah,2);

matrix_display(matrix_shrink(blah, 1, 1),2);

printf("det: %d\n", det(blah));
return 0;
}

[LaRoza]

Are you linking the the math library?

[iofthemourning]

Thanks roza. I'm used to Cygwin where that isn't necessary. My bad guys. Thanks so much!

-i

[LaRoza]

Thanks roza. I'm used to Cygwin where that isn't necessary. My bad guys. Thanks so much!

-i

That is alright. It confuses a lot of people. "-lm" isn't really intuitive, but it is needed.