Re: how to pass vector<char> as parameter?

David Wilkinson <>
Tue, 07 Aug 2007 09:03:21 -0400
Jack wrote:

I am working on a file parser.

void process_file(std::string filename)
 //FILE *afile;
 char c;

 ifstream infile(filename.c_str ());

 //if ((afile = fopen (filename, "rt")) == NULL)
 // exit(0);
  cerr<<"Can't open file " << filename << endl;

 //fileData = (char *) malloc (50000);
// memset (fileData, 0, sizeof(fileData));
// fread (fileData, sizeof(char), sizeof(fileData), afile);
 while (infile >> c)

 printf ("Parsing %s\n", filename.c_str());
    parse (fileData, fileData.size());

void parse (vector<char> buf, long count)
 int i,j;
 char *tokens[256];
 long cnt = 0; // count for number of tokens
 char c;
 bool ignore = false;
 int k = 0;

 char buff[256];
 PCSTR buf2 = &buf[0];
// char p;
 std::string buf3;
// static long token_count = 0;

 for (;;) {
  memset (buff, 0, 256);
  trim (buf2);
  is_comment(buf2[0], buf2[1]);
  if (one_line_comment)
   while (*buf2 != '\n') <<<<<<<<<<<< when I took a view at buf2, all \n
   buf2++; // Skip tail \n


1. This is happening because you use >> operator. It does not have to do
with std::vector. Use std::istream::get() like this:

while (infile.get(c))

2. How does this code compile?

PCSTR buf2 = &buf[0];
trim (buf2);

Isn't the trim function modifying buf2 here? Don't you need non-constant

char* buf2 = &buf[0];

3. You don't need to pass the size of the vector, because std::vector
knows its own size.

4. You code will not work because you are passing fileData by value. You
must pass it by reference;

void parse (vector<char>& buf, long count)

5. It is almost always best to pass standard library objects by
reference even when it is not necessary. If the object is not modified
then pass by const reference:

void process_file(const std::string& filename)

6. What is "one_line_comment? It would seem to be a global variable. It
is almost always wrong to use global variables in C++. Why not just



7. I would recommend you read a good introductory book on modern C++,
one that emphasizes (correct) usage of the standard library. You have a
lot of bad programming habits.

David Wilkinson
Visual C++ MVP

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