opening file with fopen,c\ubuntu - c

Question

Im trying to open file with fopen,and to read\write for "huffman tree".
After i've finished reading from the text, I tried to write in another file a "dictionary" that say what is the code for every letter.
I've got an eror that i havnt find something similar except that the reason is old version of eclipse, but it wasn't the problam.
Im programing in c with eclipse in ubuntu.
the main is look like:
int main(){
FILE *fsrc;
node *root;
if( (fsrc = fopen( "src.txt", "r" )) == NULL ){ //
printf( "The file 'src.txt' was not opened\n" );
return 0;
}
else {
printf( "The file 'src.txt' was opened\n" );
}
root = getBinTree(fsrc);
printTree(&(*root));
huffman(root);
return 0;
}
this is the function that writing to to target text
void printhtree(node *n,FILE *trg){
char *str = calloc(1, sizeof(char));
node *ptr=n;
while (!(ptr->m_hls && ptr->m_hrs)){
while(ptr->m_hls){
n=ptr;
ptr = ptr->m_hls;
str = realloc(1,sizeof(char)*(strlength(str)+1));
*(str+strlength(str)-1)='0';
}//while
if(!(ptr->m_hrs)){
printf("%s-%c ",str,ptr->m_ch);
n->m_hls = NULL;
return;
}//if
while(ptr->m_hrs){
n=ptr;
ptr = ptr->m_hrs;
str = realloc(1,sizeof(char)*(strlength(str)+1));
*(str+strlength(str)-1)='1';
}//while
}//while
if (!(ptr->m_ch)){
fputc(ptr->m_ch,trg);
fputc(' ',trg);
fputs(str,trg);
n->m_hls = NULL;
return;
}//if
}//printhtree
and this is the function that activate |pringhtree" function:
‪void drawTree(node *n,FILE *trg‬‬){
while(!(n))
printhtree(n,trg);
}
the error is on the first line of draw tree :
"void drawTree(node *n,FILE *trg‬‬)"
and it says:
"multiple markers at this line
bad character sequence encountered
stray '\252' in program, and the same line with the numbers 254,342,200.
there is the same error also where i wrote the names of all the function in the beginning of the program.
thank you very much

Answer 1

This is an important issue in your code
str = realloc(1,sizeof(char)*(strlength(str)+1));
For many reasons
The syntax is wrong, as it is you are realloc()ing the address 0x01.
You should not immediately overwrite the pointer, because if an error occurs then you will be unable to recover, a good usage of realloc() would be like
void *tmp = realloc(str, 1 + strlength(str));
if (tmp != NULL)
str = tmp;
This is not wrong, but it makes your code unnecessarily ugly, sizeof(char) is guaranteed to be 1.
Presumably strlength() emulates strlen(), so you don't want to compute the length twice, store it and use the value.
You allocate space the first time with malloc() but you drop that pointer completely because of the misuse of realloc() in your code, moreover you don't really need to allocate space except before writing to the pointed data, so you can replace your realloc() with malloc() and remove the calloc(), which by the way unnecessarily initialized all the values to 0, you don't need that.
You only initialize the last value of str which is set to '\0', but the rest of the data remains uninitialized because the function that would actually be allocating memory would be realloc() if it were used correctly, specially since calloc() is allocating a single byte.