Strange output while using strsep and fwrite in C

Question

I was going to make a python program to read from an XML document and use it as a reference while doing an action. However, the XML document would have been tedious to create by hand, so I decided to make a C program to do the bulk of it, excluding the first line and the root element. Here is the code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(){
    FILE * fp = fopen("/Users/rajshrimali/Desktop/SPC_CMS.txt", "r");
    FILE * fw = fopen("/Users/rajshrimali/Desktop/SPC_XML", "a");
    char *line = NULL;
    size_t linecap = 0;
    ssize_t linelen;
    while ((linelen = getline(&line, &linecap, fp)) > 0){
        char *token;
        int x = 1; 
        while((token = strsep(&line, ",")) != NULL){
            printf("%s", token);
            if(x == 1){
                fwrite("<item> \n", linelen, 1, fw);
                fwrite("<name> \n", linelen, 1, fw);
                fwrite(token, linelen, 1, fw);
                fwrite("\n </name> \n", linelen, 1, fw);
                x++; 
            }
            if(x == 2) {
                fwrite("<SPC> \n", linelen, 1, fw);
                fwrite(token, linelen, 1, fw);
                fwrite("\n </SPC> \n", linelen, 1, fw);
                fwrite("</item> \n", linelen, 1, fw);
            }
        }
    }
}

The code compiled with no errors. However, when I ran it, the file SPC_XML was not nearly right:

<item> 
�<na<name> 

 <Agate�0.80

 </name> 
�<SPC> 

 </Agate�0.80

 </SPC> 
<</item> 
,�<item> 
<na<name>

This nonsense continued for some time. The input file, fp, had data in this format:

Agate,0.80
Aluminum bronze,0.436
Aluminum,0.87
Antimony,0.21
Apatite,0.84

I think the error is with fwrite, although I have no idea what it is. What is the problem?

Shafik Yaghmour · Answer 1 · 2013-04-14T01:44:19.760

2

You have some obvious errors with your if statements here, you are using = assignment when you should be using == equality, for example:

 if(x = 1)

should be:

if(x == 1)

I would suggest turning on warning, using gcc with -Wall -W -pedantic you will see something like this:

warning: suggest parentheses around assignment used as truth value [-Wparentheses]
         if(x = 1){

edited Apr 14 '13 at 01:44

answered Apr 14 '13 at 01:37

Shafik Yaghmour

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I fixed that, same problem. – elder4222 Apr 14 '13 at 01:40
..depending of compiler you are using,turn power on the compiler-warnings. It's very very useful. :) – Jack Apr 14 '13 at 01:42

score 2 · Accepted Answer · answered Apr 14 '13 at 01:41

When you call fwrite, the second argument should be the length of the string that you are writing. So, when you do:

fwrite("<item> \n", linelen, 1, fw);

you will end up writing extra data, or maybe not enough, depending on what linelen is. Instead, you should manually count the size of your strings or call strlen on each of them. So, the call above could be turned into:

fwrite("<item> \n", 8, 1, fw);

and when you write out the tokens, you should call strlen:

fwrite(token, strlen(token), 1, fw);

Strange output while using strsep and fwrite in C

2 Answers2