help with ofstream

[McCarthy]

My assingment is to write a command line program in Unix. This program takes 3 arguments. The third argument is a generation prefix. I am suppose to print out to a text file in the format of <gen_prefix> + < generation number > + ".txt"
If the gen_prefix is "gen", then the base Generation file will be: "gen0.txt"
Generation 1 will be "gen1.txt"
Im not sure how to create or declare such a file.
Please help

[Ganon11]

Which part are you having trouble with? Getting the arguments passed to your program? Finding out the textfile name? Creating the ofstream object? Writing the data?

[McCarthy]

Which part are you having trouble with? Getting the arguments passed to your program? Finding out the textfile name? Creating the ofstream object? Writing the data?

Creating the ofstream object. I know that i have to declare the outfile by ofstream outFile, but the problem is when I want to open the outile using outFile.open(). Im not sure what to put in the parenthesis.

[ilikepython]

Creating the ofstream object. I know that i have to declare the outfile by ofstream outFile, but the problem is when I want to open the outile using outFile.open(). Im not sure what to put in the parenthesis.

You would put the name of the file you would want to open. There is also a second arguement that determines what mode you open the file in but it is only optional.

[McCarthy]

You would put the name of the file you would want to open. There is also a second arguement that determines what mode you open the file in but it is only optional.

Yea I know that i could do outFile.open("gen.txt") but since the file name depends on the third argument my program recieves plus an int that increments in the prog. as I posted above, and I know outFile.open(gen_prefix+id."txt") wont work
Im not sure how to do that.

[ilikepython]

Yea I know that i could do outFile.open("gen.txt") but since the file name depends on the third argument my program recieves plus an int that increments in the prog. as I posted above, and I know outFile.open(gen_prefix+id."txt") wont work
Im not sure how to do that.

Oh ok, I'm sorry if I misunderstood you.
You can try using strcat() and strcpy(). Strcat adds two strings together and strcpy copies a string into another:

char filename[20];
strcpy(filename, gen_prefix);
strcat(filename, gen_number);
strcat(filename, ".txt");
outFile.open(filename);
 

Does that work for you?

[McCarthy]

Oh ok, I'm sorry if I misunderstood you.
You can try using strcat() and strcpy(). Strcat adds two strings together and strcpy copies a string into another:

char filename[20];
strcpy(filename, gen_prefix);
strcat(filename, gen_number);
strcat(filename, ".txt");
outFile.open(filename);
 

Does that work for you?

For some reason the compiler is giving me an error regarding
outFile.open(filename) saying there is no matching function for call to std.basic ofstream

[Ganon11]

Is filename a string (std::string) or an array of characters? The .open() function requires an array of characters to work. If you are using a string, it can still work, but you must use filename.c_str() to make it work.