Pointer's weird behavior
Trying to run this piece of code:
void print_matrix(matrix* arg)
{
int i, j;
for(i = 0; i < arg->rows; i++) {
for(j = 0; j < arg->columns; j++) { // gdb shows, that arg->columns value
printf("\n %f", arg->data[i][j]); // has been changed in this line (was
} // 3, is 0)
printf("\n");
}
}
matrix
is a structure:
typedef struct matrix_t
{
int rows;
int columns;
double** data;
} matrix;
arg is properly allocated 3x3 matrix, rows = 3, columns = 3
Function does print only \n's .
Compiler is gcc 4.5. Any ideas?
EDIT:
int main()
{
matrix arg;
arg.rows = 3;
arg.columns = 3;
arg.data = (double**)malloc(sizeof(double*) * arg.rows);
int i;
for(i = 0; i < arg.rows; i++) {
arg.data[i] = (double*)malloc(sizeof(double) * arg.columns);
}
arg.data[0][0] = 1;
arg.data[0][1] = 2;
//......
print_ma开发者_开发百科trix(&arg);
for(i = 0; i < arg.rows; i++) {
free(arg.data[i]);
}
free(arg.data);
return EXIT_SUCCESS;
}
As mentioned in comments above, there seems to be nothing wrong with the code. Works fine when compiled on my machine and on IDEone. See http://ideone.com/SoyQH
I had a few minutes to spare, so I ran a few extra checks. These are pretty much the steps I take before each code commit or when I need some hints when debugging.
Testing with strict compiler flags
Compiling with gcc using -Wall -pedantic
there were some warnings regarding ISO C90 incompatibilities but no show stoppers.
[me@home]$ gcc -Wall -pedantic -g k.c
k.c:17:55: warning: C++ style comments are not allowed in ISO C90
k.c:17:55: warning: (this will be reported only once per input file)
k.c: In function `main':
k.c:30: warning: ISO C90 forbids mixed declarations and code
Warnings related to :
- use of C++ style comments, i.e.
//
instead of/* ... */
- in
main()
, declaration ofint i;
was mixed in with code. C90 expects all declarations to be done at the beginning.
Using split
After addressing the above warnings, ran splint -weak
on the code.
[me@home]$ splint -weak k.c
Splint 3.1.1 --- 15 Jun 2004
Finished checking --- no warnings
Nothing to report.
Valgrind
Valgrind confirms that there are no memory leaks but complains about the use of unitialised values in printf
(not all elements in args->data
were given values).
[me@home]$ valgrind ./a.out
==5148== Memcheck, a memory error detector.
... <snip> ...
==5148==
1.000000
2.000000
==5148== Conditional jump or move depends on uninitialised value(s)
==5148== at 0x63D6EC: __printf_fp (in /lib/tls/libc-2.3.4.so)
==5148== by 0x63A6C4: vfprintf (in /lib/tls/libc-2.3.4.so)
==5148== by 0x641DBF: printf (in /lib/tls/libc-2.3.4.so)
==5148== by 0x804842A: print_matrix (k.c:18)
==5148== by 0x8048562: main (k.c:42)
... <snip> ...
==5148==
==5148== ERROR SUMMARY: 135 errors from 15 contexts (suppressed: 12 from 1)
==5148== malloc/free: in use at exit: 0 bytes in 0 blocks.
==5148== malloc/free: 4 allocs, 4 frees, 84 bytes allocated.
==5148== For counts of detected errors, rerun with: -v
==5148== All heap blocks were freed -- no leaks are possible.
Conclusion
Nothing to report. Moving on.
matrix.data
is a wild pointer. You need to allocate memory for the matrix and make data
point to it.
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