错误：无法转换&#39;std :: string {aka std :: basic_string <char> 初始化时&#39;&#39;到&#39;char *&#39;

Question

I'm tinkering with C++ (I have a COBOL, Perl and PHP background) and I'm having trouble splitting a string so that I can act on each parsed field. I believe the trouble is to do with my lack of understanding of how C++ handles variables.

I've slurped a file's contents into an array successfully and I can act on each complete line (eg search/replace text). I also found some great examples of how to parse strings. The problem occurs when I try to apply the parse examples to the strings in my array.

The strings are created via:

    std::vector<std::string> File_Lines;
    ifstream file(filename.c_str());
    while ( file.good() ) {
      getline ( file, line, '\n' );
      string InputLine = string( line );
      File_Lines.push_back(line);
    }

One working example of parsing strings (that I found on this site) is:

char myString[] = "The quick brown fox";
char *p = strtok(myString, " ");
while (p) {
  printf ("Token: %s\n", p);
  p = strtok(NULL, " ");
}

The problem starts when I try to feed my string to the code that does the parsing. Feeding it directly:

char myString[] = File_Lines[array_counter];

gives "error: initializer fails to determine size of 'myString'"

If I try converting using "std::string" (as suggested in other answers on this site):

std::string File_Line;
File_Line = File_Lines[array_counter];
char myString[] = File_Line;

...I get the same error.

Other answers suggested adjusting the code to:

char *myString = File_Line;

but that just gives me "error: cannot convert 'std::string {aka std::basic_string}' to 'char*' in initialization"

I'm aware that the problem is due to my own ignorance, but I'd really appreciate any help on how to feed a string into a parser.

Also, if anyone has any simple explanation of how to convert between the data types, that would be great.

Answer 1

This should be fine:

std::string ThisLine = File_Lines[array_counter]; // make a copy for strtok to mess up
char *p = strtok(&ThisLine[0], " "); // strtok needs a pointer to the first character
while (p) {
    printf ("Token: %s\n", p);
    p = strtok(NULL, " ");
}

But C++ has nicer ways to tokenize than strtok. For example, std::strstream with operator>> (for whitespace delimiters) or getline (for delimiter you specify).

Answer 2

use the following:

const char * myString1 = File_Lines[array_counter].c_str();
char * myString=const_cast<char*>myString1;