Question on ofstream

[yeshello54]

Quick question on c++ ofstream. in my main i have it declared as int main(int arg, char*argv[]). so that when i run the following command ./program.cpp test.txt it will run my program and pass the test.txt file into it. My question is how do i save my output file as the file name i passed in. i know to use ofstream but im not sure how to pass in the file i passed into my program to test. I have the following code.any help would be great. thanks

ofstream myfile(" ", ios::out);

[Nepomuk]

The filename will be saved in the String argv[1], so just use that as the filename you give to your ofstream.

Greetings,
Nepomuk

[yeshello54]

ok i think i understand that concept. Im just not sure if im coding it right.. here is how i have tried to implement it..but it doesn not work..


int main(int arg, char *argv[]){
string fname= argv[1];
ofstream myfile( fname, ios::out);

[weaknessforcats]

You cannot use a string object as the argument.

Either do this:

int main(int arg, char *argv[]){
ofstream myfile( argv[1], ios::out); 

or do this:

int main(int arg, char *argv[]){
string fname= argv[1];
ofstream myfile( fname.c_str(), ios::out); 

[Banfa]

Also before you do anything with argv[1] you should check that argc > 1 otherwise you will be using a NULL pointer.

[yeshello54]

so i get the following error ...
"terminate called after throwing an instance of 'std::bad_alloc'
what(): St9bad_alloc
Abort trap

not sure why but it might have to do with me passing the argc into my parser function.??



this is the code i have.

int main(int argc, char *argv[]){

string fname= argv[1];
ofstream myfile(fname.c_str(), ios::out);

string c = argv[1];
file_parser parser(c);

[weaknessforcats]

Odd you would get a run-time error on code that won't compile:

string c = argv[1];
file_parser parser(c); 

That call to parser looks like it returns a file_parser variable. If so the call should be:

string c = argv[1];
file_parser x = parser(c); 

[yeshello54]

well before i started trying to pass the argument as the file name to be saved the following code compiled and ran just fine...

int main(int argc, char *argv[]){

string c = argv[1];
file_parser parser(c);
parser.read_file();


but i am confused by your following code...

string c=argv[1];
file_parser x (c);

[Banfa]

This

file_parser parser(c);

and this

file_parser x (c);

are exquivilent. One creates avariable called parser the other creates a variable called x.

[weaknessforcats]

file_parser parser(c);

and this

file_parser x (c);

are exquivilent. One creates avariable called parser the other creates a variable called x.

The OP says that parser is a function and not a variable. See Post #6.

[Banfa]

@weaknessforcats
No he says he has a parser function, not a function called parser. Nit picky I know but that then makes sense of the code :D

[yeshello54]

ya guys im not sure why i keep getting this problem..but let me give you a more detailed run down..

my project works fine when i give ofstream a string to name the file..
so the code looks like this.. ofstream myfile("file.lis", ios::out);

then down the road a bit i do

string c = argv[1];
where argv[1] is the file i am calling when i type the following command..
"./sicxe_asm test.asm"

then i have

file_parser parser(c);
this is my constructor that takes a file name as a string.

then i call my actual parser function

parser.read_file();
and everything wroks fine.


but if i try to pass argv[1] in the ofstream i get the crazy mem allocation error
so this code does not work for me..
string fname=argv[1];
ofstream myfile(fname.c_str(), ios::out)

so hopefully that helps explain my problem. i dont know whats wrong. but thanks for all the help so far.

[yeshello54]

just wanted to post my solution to my problem. after a bit of reading and refreshing on pointers, I was able to solve my problem with the following code..

filename= *argv[1];
for(int i=0;i<filename.length();i++)
{
filename=argv[1]
)

ofstream myfile(filename.c_str(), ios::out);


and this worked for me. I used the for loop to iterate from the starting positon of *argv[1] and increment to get my whole word i was looking for.

thanks for all of your help

--Anthony