character strings and reading in a file...

if anyone could help me and tell me what's wrong or give me some hints...

I am trying to read in a file called "data" using a function called "readfile", but I keep getting "segmentation fault (core dumped)" when I run my program.

Here is my code (I have commented out some parts of it because I just want to get the reading in a file working first):

#include <stdio.h>
#include <string.h>
#define SIZE 100

int readfile(char *filename, char *names [], int numbers [] );
/*void nametoupper(char name [] );
void sortbyname(char *names [], int numbers [], int size );
void sortbynumber(char *names [], int numbers [], int size );
void swap(char *string1, char *string2);
void printall(char *names [], int numbers [], int size );
*/
int main ()
{
char *filename;
char *names [50];
int name;
int numbers [SIZE];

printf("Type the name of the file to be sorted:\n");
scanf("%s", filename);

readfile(filename, names, numbers);
/*nametoupper( names );
sortbyname( names, numbers, size );
printall( names, numbers, size );

printf("Press any key to continue:\n");
getchar ();
sortbynumber( names, numbers, size );
printall( names, numbers, size );
*/
return 0;
}

Here is the readfile function code:
#include <stdio.h>
#include <stdlib.h>

int parseline(const char *text, char **name, int *num);

int readfile(const char *filename, char *names[], int numbers[])
{

FILE *fp;
char textline[256];
char *status;
int countlines = 0;
int len;
int linestat;

/* Try to open the file, bail out if it can't be done */
fp = fopen(filename,"r");
if (fp == NULL) {
fprintf(stderr,"Unable to open file %s\n",filename);
exit(1);
}

status = fgets(textline, 255, fp);
while (status != NULL) {
len = strlen(textline);
if (textline[len-1] == '\n') {
textline[len-1] = '\0';
}
linestat = parseline(textline,&(names[countlines]),&(numbers[countlines]));
if (linestat != -1) {
countlines += 1;
}
status = fgets(textline, 255, fp);
}

return(countlines);
}

int parseline(const char *text, char **name, int *num) {

int last;
int index;

last = strlen(text) - 1;
index = last;
while ((isspace(text[index])) && (index >= 0)) {
index -= 1;
}
while ((isdigit(text[index])) && (index >= 0)) {
index -= 1;
}

if ((index > 0) && (index < last)) {
*num = atoi(&(text[index+1]));
*name = (char *) malloc((index+2)*sizeof(char));
strncpy(*name,text,index+1);
(*name)[index+1] = '\0';
return 0;
} else {
fprintf(stderr,"Warning: this line is not in the right format\n %s\n",text);
return -1;
}
}

And here is the "data" I want to input as the filename to be sorted:

Chad Lewis 15
Sean Lowe 23
Harold Dane 46
Sam Zane 34
Shiki Lars 89


If anyone could help me....

Thanks,
Newbie

char *names [50];

This line creates an array of 50 pointers. It does NOT allocate the memory for those pointers. So when you tried to write to them, you accessed protected memory and crashed. Add these lines before your call to readline:

Code:

---

int x;
for(x=0;x<50;x++){
  names[x]=malloc(256*sizeof(char));
  if(names[x]==NULL){
      return 0;  /*error*/
    }
}

---

Note that even this is not safe- if there are more than 50 lines in the file, or if there are fewer, but lines are over 255 characters. A safer way would be to make either:

1)Low flexibility: readfile take a max # of lines, and dump any overage. This can be a max defined by readfile, or taken as a parameter.

2)Medium flexibility: Write a function to count the number of lines, and return the size of the file. Make names a char **,. and allocate the needed number of pointers, then allocate each line pointer.

3)Max flexibility: Make 2 new functions. Function 1 gets file length in lines, function 2 gets the length of each line, so no lines over 255 chars are wrapped. Function 3 will write to buffers for each line. Using this method you can minimize memory waste and eliminate any chance of problems. It is the slowest, however.

Thanks for the explanation and the info, but I am still getting a segementation fault error....

So post your new code. And remember. Use code tags:

[code]
... your code here ...
[/code]

Quzah.

Or I could be a complete moron and miss your real problem completely.

Code:

---

char *filename;
char *names [50];
int name;
int numbers [SIZE];

printf("Type the name of the file to be sorted:\n");
scanf("%s", filename);

---

You never allocated space for filename. Either malloc it some memory, or use an array instead.

Also, its considered very odd and poor style for a function to return dynamically allocated memory to the caller, like you do in parseline. The reason being that people will frequently forget to free the memory, causing a leak. It also makes the cause of error difficult to track down, as you don't know who the owner is. The normal method is to pass memory down to the called functions.

Here is my current code:
---------------------------------------------------------------------------------
#include <stdio.h>
#include <string.h>
#define SIZE 100

int readfile(char *filename, char *names [], int numbers [] );
/*void nametoupper(char name [] );
void sortbyname(char *names [], int numbers [], int size );
void sortbynumber(char *names [], int numbers [], int size );
void swap(char *string1, char *string2);
void printall(char *names [], int numbers [], int size );
*/
int main ()
{
char *filename;
char *names;
int name;
int numbers [SIZE];
int x;

printf("Type the name of the file to be sorted:\n");
scanf("%s", filename);

for(x=0;x<50;x++){
names[x]=malloc(256*sizeof(char));
if(names[x]==NULL){
return 0; /*error*/
}
}
readfile(filename, names, numbers);
/*nametoupper( names );
sortbyname( names, numbers, SIZE );
printall( names, numbers, SIZE );

printf("Press any key to continue:\n");
getchar ();

sortbynumber( names, numbers, SIZE );
printall( names, numbers, SIZE );
*/
return 0;
}
----------------------------------------------------------------------------------

Take a gander at Javariel's reply. Then take a look at mine, which shows how to use code tags.

Quzah.

Sorry about the code tags...I am new to this forum....

I tried allocating space to both filename and names using Javariel's method....but I still get a segmentation fault. We have just started to learn about pointers in class, so bare with me I am just a beginner.

This is what I tried:

Code:

---


#include <stdio.h>
#include <string.h>
#define SIZE 100

int readfile(char *filename, char *names [], int numbers [] );
/*void nametoupper(char name [] );
void sortbyname(char *names [], int numbers [], int size );
void sortbynumber(char *names [], int numbers [], int size );
void swap(char *string1, char *string2);
void printall(char *names [], int numbers [], int size );
*/
int main ()
{
char *filename;
char *names;
int name;
int numbers [SIZE];
int x, y;

printf("Type the name of the file to be sorted:\n");
scanf("%s", filename);

for(x=0;x<50;x++){
  names[x]=malloc(256*sizeof(char));
  if(names[x]==NULL){
      return 0;  /*error*/
    }
}
for(y=0;y<50;y++){
  filename[y]=malloc(256*sizeof(char));
  if(filename[y]==NULL){
      return 0;  /*error*/
    }
}


readfile(filename, names, numbers);
/*nametoupper( names );
sortbyname( names, numbers, SIZE );
printall( names, numbers, SIZE );
 
printf("Press any key to continue:\n");
getchar ();

sortbynumber( names, numbers, SIZE );
printall( names, numbers, SIZE );
*/
return 0;
}

---

Code:

---

char *filename;
char *names;
int name;
int numbers [SIZE];
int x, y;

printf("Type the name of the file to be sorted:\n");
scanf("%s", filename);

---

You still have no space allocated for the file name. Try something like:

char filename[BUFSIZ];

... stuff here ...

printf("Type the name of the file to be sorted:\n");
fgets( filename, BUFSIZ, stdin );
filename[strlen(filename)-1] = '\0';

That should do the trick. fgets is a safe way to read strings. It will only read "one less than the size you indicate" characters, and it will add a null to the end. The only thing to remember is that if you have a newline (return) on the end of the string, you'll want to snip it off. That's what the last line of code does.

'stdin' is the standard input file stream, or in other words, the keyboard. Since I used 'f'-gets, I needed to specify a file to read from. On a side note, never just use 'gets'. It's unsafe.

Quzah.

Thanks for your help quzah, but even with the changes from your suggestions, I still get a segmentation fault....and this warning warning: passing arg 2 of `readfile' from incompatible pointer type

This is what I tried:

Code:

---



#include <stdio.h>
#include <string.h>
#define SIZE 100
#define BUFSIZ 50

int readfile(char *filename, char *names [], int numbers [] );
/*void nametoupper(char name [] );
void sortbyname(char *names [], int numbers [], int size );
void sortbynumber(char *names [], int numbers [], int size );
void swap(char *string1, char *string2);
void printall(char *names [], int numbers [], int size );
*/
int main ()
{

char filename[BUFSIZ];
char *names;
int name;
int numbers [SIZE];
int x;

printf("Type the name of the file to be sorted:\n");
fgets( filename, BUFSIZ, stdin );
filename[strlen(filename)-1] = '\0';

for(x=0;x<50;x++){
  names[x]=malloc(256*sizeof(char));
  if(names[x]==NULL){
      return 0;  /*error*/
  }
}

readfile(filename, names, numbers);
/*nametoupper( names );
sortbyname( names, numbers, SIZE );
printall( names, numbers, SIZE );

printf("Press any key to continue:\n");
getchar ();

sortbynumber( names, numbers, SIZE );
printall( names, numbers, SIZE );
*/
return 0;
}

---

That's because you're not passing it correct arguments:

int readfile(char *filename, char *names [], int numbers [] );


And you pass it:

char *names;


You need an array of character poitners, not just a character pointer.

char *names[SOMENUMBER];

That'll fix it.

Quzah.

Thanks Quzah, it works now...I can finally read in a file.

Now if I could only get my other functions to work. *L*
My professor did say pointers could be a nightmare....

Hi again,

I was wrong...it didn't exactly work. Now I am getting the segmentating fault error again. If anyone could help me again.... It compiles with no errors and no warnings....but I am thinking it is a pointer problem... I am so lost.

Here is what I have now:
[code]
#include <stdio.h>
#include <string.h>
#define SIZE 100

/*function prototypes*/
/*int readfile(char *filename, char *names [], int numbers [] );
void nametoupper(char *names [] );
void sortbyname(char *names [], int numbers [], int size );
void sortbynumber(char *names [], int numbers [], int size );
void swap(char *string1, char *string2);
void printall(char *names [], int numbers [], int size );
*/
int main ()
{

/*declaration of variables*/
char filename [BUFSIZ];
char *names [SIZE];
int name;
int numbers [SIZE];

/*prompt user for filename*/
printf("Type the name of the file to be sorted:\n");

/*read in filename*/
fgets( filename, BUFSIZ, stdin );

filename[strlen(filename)-1] = '\0';
/*call functions*/
readfile(filename, names, numbers);
/*nametoupper(names );
sortbyname( names, numbers, SIZE );
printall( names, numbers, SIZE );

/*pause in the program*/
printf("Press any key to continue:\n");
getchar ();

sortbynumber( names, numbers, SIZE );
printall( names, numbers, SIZE );
*/
return 0;
} /*end main*/

Is this all of your code? Because you can't call functions that don't have a definition.

-Prelude

sorry ... I didn't post all of my code with the definitons of the other functions. I have commented out the other functions because I just want to get reading in a file to work first.

the readfile code is in my first post... It is a separate file, that I link with my main code to compile.