asked on

Append a string to a file

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

jmsloan

ASKER

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();

ASKER CERTIFIED SOLUTION

Axter

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rstaveley

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<--------