getting rid of newline?

[KBriggs]

#define LINE_MAX 1024
#include<string.h>
#include<stdio.h>
#include<stdlib.h>

char *find_param( char *buffer, int buffersize, const char *param_name, 
		  FILE *stream )
{
    char *hash;
    char *value;
    char *equal;
    
    // reset stream to beginning of file (with SEEK_SET + 0 offset)
    fseek( stream, 0, SEEK_SET);
    
    while( ( fgets( buffer, buffersize, stream ) ) != (char *)0 ){
	
	// get rid of all comments, preceeded by a # symbol
	hash = index(buffer,'#');
	if( hash != NULL ){
	    *hash = '\0';
	}
	
	// check if we find '=' in current line in buffer
	// if there isn't one in this line, go to next line
	equal = index(buffer,'=');
	if( equal == NULL ) 
	    continue;
	
	// set start of value (pointer arithmetic) in case there is a match
	value = equal + 1;
	
	// cut off string at '=' for string comparison
	*equal = '\0';
	
	// compare cut off string in buffer to param_name sought
	// if they agree, return the pointer
	if( strcmp( buffer, param_name) == 0 ) {
	    return(value);
	}
	
   }
    
    return(NULL);
}


char *get_str_param(const char *param_name, FILE *stream )
{
   char *buffer;
   char *value_pointer;
    char *equal;
    int i;
   // set buffer size for input file lines
   if( ( buffer = (char *) calloc( LINE_MAX, sizeof(char))) == NULL ){
       fprintf(stderr,"error in get_str_param: calloc failed");
       exit(1);
   }
   
   // find pointer to parameter value, (pointer to char array)
   if( ( value_pointer = find_param( buffer, LINE_MAX, param_name, stream ) )
       == NULL ){
       fprintf(stderr,"error in get_str_param: ");
       fprintf(stderr,"Didn't find parameter %s in input file\n", param_name );
       exit(1);
   }
   
   
   free(buffer);
   
   return(value_pointer);
}

int main()
{
  char *param;
  char input_file_name[100] = "input_test.txt";
  FILE *input;
  input = fopen(input_file_name,"r");
  if (input == NULL)
  {
    printf("file open failed\n");
    abort();
  }
  param = get_str_param("source",input);
  printf("%s",param);
}

The functions above are part of a larger code, I just wrote main here to test a new one, that is supposed to read a string from an input file of format:

parameter=string

The code is supposed to go through the file, find parameter, and return the string that comes after the equal sign.


It works! However, for some reason when it prints out, there is a newline being printed (or possible just lots of whitespace, I can't tell. To get rid of it, I tried:

equal = index(value_pointer,'\n');
   if( equal != NULL )
   {
     equal = '\0';
   }

in get_str_param just before freeing buffer, but it makes no difference. Could someone point me in the direction of my mysterious newline?

Thanks

[laserlight]

fgets() stores the newline read, if there is space for it. Use strchr() to find it, and if the newline is found, set it to be a null character.

[KBriggs]

I added this:

   char *temp;
   temp = strchr(value_pointer,'\n');
   if(temp!=NULL)
   {
     temp = '\0';
   }

to no effect

Manually setting

//value_pointer[(int) strlen(param)-1]='\0';

works, though. I am really not familiar with manipulation of strings in general, I must be doing something silly here.

[GL.Sam]

>temp = '\0';
Let me guess. It has had no effect because you forgot to dereference a pointer.

Also,
>(int)
is not necessary.

[KBriggs]

Yeah, I just figured that out ^_^

Been a while since I used C

Thanks

The cast to int made my compiler stop complaining about giving %d a size_t, but yes, it is not strictly necessary

[laserlight]

The cast to int made my compiler stop complaining about giving %d a size_t, but yes, it is not strictly necessary

Use %u or %lu instead.

[KBriggs]

I ended up using

   for (i = 0; i < strlen(value_pointer); i++)
   {
     temp = value_pointer+i;
     if(isspace(*temp))
     {
       *temp = '\0';
     }
   }

to get rid of all the whitespace possibilities - will be fine as long as I keep the input parameters to one word, which they are anyway.

Thanks everyone

[laserlight]

Save the result of strlen instead of calling it in a loop. Once you have dealt with such a whitespace character, you can break from the loop as there is no point setting null characters further down in the string since the string would have already been truncated.

Incidentally, you could also use strpbrk as a substitute for strchr, though you would then have to explicitly specify the whitespace characters instead of relying on isspace.

[KBriggs]

   length = (int) strlen(value_pointer);
   for (i = 0; i < length; i++)
   {
     temp = value_pointer+i;
     if(isspace(*temp))
     {
       *temp = '\0';
       break;
     }
   }

I don't think it will add anything significant to the speed of the process since the files are typically no more than 100 lines long with two words per line, but I guess it is good practice ^_^

[laserlight]

I suggest writing it this way:

size_t i, length;

length = strlen(value_pointer);
for (i = 0; i < length; i++)
{
    if (isspace(value_pointer[i]))
    {
        value_pointer[i] = '\0';
        break;
    }
}

[Kennedy]

Then there is this way:

char *st;
st = value_pointer;
while (st){
        if (isspace(st[0]){
                st[0] = '\0';
                break;
        }
        st++;
}