Output wrong. Possible strncpy issue? - c++

Question

So, I'm trying to get this code to parse each line inputted from the file into individual tokens, then add each one in turn to tklist array. Then the main just prints out each token. It's printing blanks though, and when I step into the code it looks like the strncpy isn't working. Any ideas what the issue is? I get no errors.
Here's the main function:
#include <iostream>
#include <fstream>
using namespace std;
#include "definitions.h"
#include "system_utilities.h"
int main()
{
ifstream inFile;
char line[MAX_CMD_LINE_LENGTH];
char* token[MAX_TOKENS_ON_A_LINE];
int numtokens;
system("pwd");
inFile.open("p4input.txt", ios::in);
if(inFile.fail()) {
cout << "Could not open input file. Program terminating.\n\n";
return 0;
}
while (!inFile.eof())
{
inFile.getline(line, 255);
line[strlen(line)+1] = '\0';
numtokens = parseCommandLine(line, token);
int t;
for (t=1; t <= numtokens; t++) {
cout << "Token "<< t << ": " << token[t-1] << "\n";
}
}
return 0;
}
And here's the parseCommandLine function:
int parseCommandLine(char cline[], char *tklist[]){
int i;
int length; //length of line
int count = 0; //counts number of tokens
int toklength = 0; //counts the length of each token
length = strlen(cline);
for (i=0; i < length; i++) { //go to first character of each token
if (((cline[i] != ' ' && cline[i-1]==' ') || i == 0)&& cline[i]!= '"') {
while ((cline[i]!=' ')&& (cline[i] != '\0') && (cline[i] != '\r')){
toklength++;
i++;
}
//---------------
tklist[count] = (char *) malloc( toklength +1);
strncpy(tklist[count], &cline[i-toklength], toklength);
//--------------
count ++;
toklength = 0;
}
if (cline[i] == '"') {
do {
toklength++;
i++;
if (cline[i] == ' ') {
toklength--;
}
} while (cline[i]!='"');
//--------------
tklist[count] = (char *) malloc( toklength +1);
strncpy(tklist[count], &cline[i-toklength], toklength);
//--------------
count ++;
toklength = 0;
}
}
int j;
for (j = 0; j < count; j++) {
free( (void *)tklist[j] );
}
return count;
}
Like I said, when I debug it looks like a problem with copying, but I'm a beginner so I suspect I'm doing something wrong.
Thanks for any help you can give!!

Answer 1

Try something like
tklist[count][toklength]='\0';
after
strncpy(tklist[count], &cline[i-toklength], toklength);
strncpy() does not necessarily add a null terminator for you. strncpy needs some care to use safely.
No null-character is implicitly appended at the end of destination if
source is longer than num..
Just for starters... there are other deeper issues as mentioned in comments.

Answer 2

To start with the generic equivalent of malloc/free is new/delete (heap memory allocation).
Second you seem to be confusing strings and c_strings (good old char*). getline uses strings, your parsing function uses c_strings they are not the same things and there is .c_str() a member function of string to do the conversion.

Answer 3

So, I'm trying to get this code to parse each line inputted from the
file into individual tokens, then add each one in turn to tklist
array.
For
each line inputted from the file
use
std::ifstream ifs;
std::string s;
/**/
std::getline(ifs, s);
adopted to your loop.
To
parse [..] into individual tokens
look how
std::string
can help you on that task (or use boost::tokenizer).
And this
then add each [token] in turn to tklist array.
almost cries for std::list or std::vector instead of a plain C array, the choice, which container to use depends e.g. on what you intend to do with the tokens found.