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Append a string to a file

Posted on 2004-04-27
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Last Modified: 2008-03-03
Hello I am trying to create a string variable and append that variable on another line of an open file.

Here is what I have so far

     strftime(var, 30, "%m%d", tm_data);
     string tmpfilename(var);
     journalfile = "C:\\hlmkejrnl\\" + tmpfilename + ".txt";

     // open file with a MMDDhhmmss.txt format to save transaction
        ofstream outfile (journalfile.c_str(), ios::app);

         string ejrnlfile = "Hope this works";
          outfile.write(ejrnlfile);
          outfile.close();

"Hope this works" should append to the file MMDD.txt file, but I get an error

Cannot convert 'string' to 'const char *' in function main()

and

Type mismatch in parameter 's' (wanted 'const char *', got 'string') in function main()

Maybe there would be a better way to open a file and append a string to it?  

Any suggestions?

Thanks,

jmsloan
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Question by:jmsloan
3 Comments
 
LVL 3

Author Comment

by:jmsloan
ID: 10929887
I believe I figured it out.  I did this and it seems to work

     strftime(var, 30, "%m%d", tm_data);
     string tmpfilename(var);
     journalfile = "C:\\hlmkejrnl\\" + tmpfilename + ".txt";

     // open file with a MMDDhhmmss.txt format to save transaction
        ofstream outfile (journalfile.c_str(), ios::app);

         string ejrnlfile = "Hope this works\n";
         outfile << ejrnlfile;
         outfile.close();
0
 
LVL 30

Accepted Solution

by:
Axter earned 50 total points
ID: 10929900
>>Cannot convert 'string' to 'const char *' in function main()

Do the following instead:
outfile << ejrnlfile;
0
 
LVL 17

Expert Comment

by:rstaveley
ID: 10930447
Axter and jmsloan are absolutely right, but for the record if you do want a pointer to a char* for a legacy C function, you should copy the std::string into std::vector<char> and '\0'-terminate it.

e.g.
--------8<--------
#include <cstdio> // For yucky old printf
#include <string>
#include <vector>

int main()
{
      std::string str = "Hello world";

      std::vector<char> v(str.begin(),str.end());
      v.push_back('\0'); // C strings need '\0' termination

      std::printf("C programmers like to say \"%s\"",&v[0]);
}
--------8<--------
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