Programming Forums > Application Development > C

Planet_EN · Mar 24th, 2007, 3:49 AM

I dont know whats terribly going wrong with this, well I know there's some memory allocation with this but I tried hard to fix it and when it gets fixed it doesn't shows up the desired value, this is the code that shows the compile-time error:

(Toggle Plain Text)

#include <stdio.h>
#include <string.h>

#define $WORD_LIST(X) "resource/" X

typedef struct char_type
{
	char** ptr;
}ccarray;

int ccarray_create(ccarray *c)
{
	c = (ccarray*)malloc(sizeof(ccarray*));
	
	c->ptr = (char**) malloc(sizeof(char**) * 1024);
	return 0;
}

int ccarray_insert(ccarray *c, char* str, int pos)
{
	c->ptr[pos] = str;
	printf("%d %s\n", pos, c->ptr[pos]);
}

int ccarray_destroy(ccarray *c)
{
	free( c->ptr );
	free( c );
	return 0;
}

int ccarray_read_file(ccarray* c, char* filename)
{
	FILE * fptr;
	char* line;
	int i;
	
	fptr = fopen(filename, "r");
	line = (char*) malloc(sizeof(char)*100);
	i = 0;
	
	while( fscanf(fptr,"%s",line) != EOF )
	{
		ccarray_insert(c, line, i);
		i++;
	}
	free(line);
	fclose(fptr);
}

int ccarray_print(ccarray* c)
{
	int i = 0;
	while ( c->ptr[i] != NULL )
	{
		printf("Line: %s\n", c->ptr[i] );
		i++;
	}
}

int main()
{
	ccarray * c;
	ccarray_create(c);
	ccarray_read_file(c, $WORD_LIST("sample.txt"));
	ccarray_print(c);
	ccarray_destroy(c);
	return 0;
}

... and this thing runs fine but doesn't shows any result:

(Toggle Plain Text)

#include <stdio.h>
#include <string.h>

#define $WORD_LIST(X) "resource/" X

typedef struct char_type
{
	char** ptr;
}ccarray;

int ccarray_create(ccarray **c)
{
	(*c) = (ccarray*)malloc(sizeof(ccarray));
	(*c) = (ccarray*)malloc(sizeof(ccarray));
	(*c)->ptr = (char**) malloc(sizeof(char**) * 1024);
	return 0;
}

int ccarray_insert(ccarray **c, char* str, int pos)
{
	(*c)->ptr[pos] = str;
	//printf("%s ", (*c)->ptr[pos] );
}

int ccarray_destroy(ccarray **c)
{
	free( (*c)->ptr );
	free( c );
	return 0;
}

int ccarray_read_file(ccarray** c, char* filename)
{
	FILE * fptr;
	char* line;
	int i;
	
	fptr = fopen(filename, "r");
	line = (char*) malloc(sizeof(char)*100);
	i = 0;
	
	while( fscanf(fptr,"%s",line) != EOF )
	{
		ccarray_insert(c, line, i);
		i++;
	}
	free(line);
	fclose(fptr);
}

int ccarray_print(ccarray** c)
{
	int i = 0;
	while ( (*c)->ptr[i] != NULL )
	{
		printf("Line: %s\n", (*c)->ptr[i] );
		i++;
	}
}

int main()
{
	ccarray * c;
	ccarray_create(&c);
	ccarray_read_file(&c, $WORD_LIST("sample.txt"));
	ccarray_print(&c);
	ccarray_destroy(&c);
	return 0;
}

grumpy · Mar 24th, 2007, 5:27 AM

It is usually helpful to provide SMALL code fragments that exhibit your problem, describe your problem clearly (eg what you expect to see vs what you see, what compiler errors, etc). Otherwise, the help you get will be limited.

Both of your code fragments will yield compile errors as;

(Toggle Plain Text)

#define $WORD_LIST(X) "resource/" X

is invalid. Identifiers are not allowed to start with a dollar sign.

Assuming you've somehow got past that with a compiler extension, the basic issue is that you are not understanding how pointers work or how arguments are passed by value to functions.

For example, in your first block of code;

(Toggle Plain Text)

int ccarray_create(ccarray *c)
{
	c = (ccarray*)malloc(sizeof(ccarray*));
	
	c->ptr = (char**) malloc(sizeof(char**) * 1024);
	return 0;
}

int main()
{
    ccarray *c;
    ccarray_create(c);
    ccarray_read_file(c, $WORD_LIST("sample.txt"));
}

The variable c in ccarray_create() is not the same as in main(). The changes to c within ccarray_create() are local to that function, and not visible to main(). So, when you call ccarray_read_file(), you are still passing an unitialised value to ccarray_read_file(), which dereferences that pointer.

The result is undefined behaviour by the bucket full.
- Even copying an uninitialised variable yields undefined behaviour (which is what happens simply by passing it by value to a function)
- Dereferencing an uninitialised pointer also yields undefined behaviour.

bl00dninja · Mar 25th, 2007, 3:38 AM

the point here is, if you submit 1,000 lines of code only the really good guys will look at it. i do this myself when my back is against a wall, so i'm NOT bitching at you. however, if you know WHERE your problem is, point it out with some relevant context.

good luck!

Mar 24th, 2007, 3:49 AM	#1
Planet_EN Programmer Join Date: Mar 2005 Posts: 40 Rep Power: 0	Bugging ... Compile Time Error I dont know whats terribly going wrong with this, well I know there's some memory allocation with this but I tried hard to fix it and when it gets fixed it doesn't shows up the desired value, this is the code that shows the compile-time error: (Toggle Plain Text) #include <stdio.h> #include <string.h> #define $WORD_LIST(X) "resource/" X typedef struct char_type { char** ptr; }ccarray; int ccarray_create(ccarray c) { c = (ccarray)malloc(sizeof(ccarray)); c->ptr = (char) malloc(sizeof(char) 1024); return 0; } int ccarray_insert(ccarray c, char str, int pos) { c->ptr[pos] = str; printf("%d %s\n", pos, c->ptr[pos]); } int ccarray_destroy(ccarray c) { free( c->ptr ); free( c ); return 0; } int ccarray_read_file(ccarray c, char* filename) { FILE * fptr; char* line; int i; fptr = fopen(filename, "r"); line = (char) malloc(sizeof(char)100); i = 0; while( fscanf(fptr,"%s",line) != EOF ) { ccarray_insert(c, line, i); i++; } free(line); fclose(fptr); } int ccarray_print(ccarray* c) { int i = 0; while ( c->ptr[i] != NULL ) { printf("Line: %s\n", c->ptr[i] ); i++; } } int main() { ccarray * c; ccarray_create(c); ccarray_read_file(c, $WORD_LIST("sample.txt")); ccarray_print(c); ccarray_destroy(c); return 0; } #include <stdio.h> #include <string.h> #define $WORD_LIST(X) "resource/" X typedef struct char_type { char** ptr; }ccarray; int ccarray_create(ccarray c) { c = (ccarray)malloc(sizeof(ccarray)); c->ptr = (char) malloc(sizeof(char) 1024); return 0; } int ccarray_insert(ccarray c, char str, int pos) { c->ptr[pos] = str; printf("%d %s\n", pos, c->ptr[pos]); } int ccarray_destroy(ccarray c) { free( c->ptr ); free( c ); return 0; } int ccarray_read_file(ccarray c, char* filename) { FILE * fptr; char* line; int i; fptr = fopen(filename, "r"); line = (char) malloc(sizeof(char)100); i = 0; while( fscanf(fptr,"%s",line) != EOF ) { ccarray_insert(c, line, i); i++; } free(line); fclose(fptr); } int ccarray_print(ccarray* c) { int i = 0; while ( c->ptr[i] != NULL ) { printf("Line: %s\n", c->ptr[i] ); i++; } } int main() { ccarray * c; ccarray_create(c); ccarray_read_file(c, $WORD_LIST("sample.txt")); ccarray_print(c); ccarray_destroy(c); return 0; } ... and this thing runs fine but doesn't shows any result: (Toggle Plain Text) #include <stdio.h> #include <string.h> #define $WORD_LIST(X) "resource/" X typedef struct char_type { char ptr; }ccarray; int ccarray_create(ccarray c) { (c) = (ccarray)malloc(sizeof(ccarray)); (c) = (ccarray)malloc(sizeof(ccarray)); (c)->ptr = (char) malloc(sizeof(char) 1024); return 0; } int ccarray_insert(ccarray *c, char str, int pos) { (c)->ptr[pos] = str; //printf("%s ", (c)->ptr[pos] ); } int ccarray_destroy(ccarray *c) { free( (c)->ptr ); free( c ); return 0; } int ccarray_read_file(ccarray** c, char* filename) { FILE * fptr; char* line; int i; fptr = fopen(filename, "r"); line = (char) malloc(sizeof(char)100); i = 0; while( fscanf(fptr,"%s",line) != EOF ) { ccarray_insert(c, line, i); i++; } free(line); fclose(fptr); } int ccarray_print(ccarray** c) { int i = 0; while ( (c)->ptr[i] != NULL ) { printf("Line: %s\n", (c)->ptr[i] ); i++; } } int main() { ccarray * c; ccarray_create(&c); ccarray_read_file(&c, $WORD_LIST("sample.txt")); ccarray_print(&c); ccarray_destroy(&c); return 0; } #include <stdio.h> #include <string.h> #define $WORD_LIST(X) "resource/" X typedef struct char_type { char ptr; }ccarray; int ccarray_create(ccarray c) { (c) = (ccarray)malloc(sizeof(ccarray)); (c) = (ccarray)malloc(sizeof(ccarray)); (c)->ptr = (char) malloc(sizeof(char) 1024); return 0; } int ccarray_insert(ccarray *c, char str, int pos) { (c)->ptr[pos] = str; //printf("%s ", (c)->ptr[pos] ); } int ccarray_destroy(ccarray *c) { free( (c)->ptr ); free( c ); return 0; } int ccarray_read_file(ccarray** c, char* filename) { FILE * fptr; char* line; int i; fptr = fopen(filename, "r"); line = (char) malloc(sizeof(char)100); i = 0; while( fscanf(fptr,"%s",line) != EOF ) { ccarray_insert(c, line, i); i++; } free(line); fclose(fptr); } int ccarray_print(ccarray** c) { int i = 0; while ( (c)->ptr[i] != NULL ) { printf("Line: %s\n", (c)->ptr[i] ); i++; } } int main() { ccarray * c; ccarray_create(&c); ccarray_read_file(&c, $WORD_LIST("sample.txt")); ccarray_print(&c); ccarray_destroy(&c); return 0; }

Mar 24th, 2007, 5:27 AM	#2
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,198 Rep Power: 5	It is usually helpful to provide SMALL code fragments that exhibit your problem, describe your problem clearly (eg what you expect to see vs what you see, what compiler errors, etc). Otherwise, the help you get will be limited. Both of your code fragments will yield compile errors as; (Toggle Plain Text) #define $WORD_LIST(X) "resource/" X #define $WORD_LIST(X) "resource/" X is invalid. Identifiers are not allowed to start with a dollar sign. Assuming you've somehow got past that with a compiler extension, the basic issue is that you are not understanding how pointers work or how arguments are passed by value to functions. For example, in your first block of code; (Toggle Plain Text) int ccarray_create(ccarray c) { c = (ccarray)malloc(sizeof(ccarray)); c->ptr = (char) malloc(sizeof(char) 1024); return 0; } int main() { ccarray c; ccarray_create(c); ccarray_read_file(c, $WORD_LIST("sample.txt")); } int ccarray_create(ccarray c) { c = (ccarray)malloc(sizeof(ccarray)); c->ptr = (char) malloc(sizeof(char) * 1024); return 0; } int main() { ccarray *c; ccarray_create(c); ccarray_read_file(c, $WORD_LIST("sample.txt")); } The variable c in ccarray_create() is not the same as in main(). The changes to c within ccarray_create() are local to that function, and not visible to main(). So, when you call ccarray_read_file(), you are still passing an unitialised value to ccarray_read_file(), which dereferences that pointer. The result is undefined behaviour by the bucket full. - Even copying an uninitialised variable yields undefined behaviour (which is what happens simply by passing it by value to a function) - Dereferencing an uninitialised pointer also yields undefined behaviour.

Mar 25th, 2007, 3:38 AM	#3
bl00dninja Programming Guru Join Date: Oct 2004 Location: namespace std Posts: 1,246 Rep Power: 5	the point here is, if you submit 1,000 lines of code only the really good guys will look at it. i do this myself when my back is against a wall, so i'm NOT bitching at you. however, if you know WHERE your problem is, point it out with some relevant context. good luck! __________________ i put on my robe and wizard hat... Have you ever heard of Plato, Aristotle, Socrates?...Morons.

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Programming Forums > Application Development > C

Bugging ... Compile Time Error