How can I create array of files in C/C++?

Question

In a C/C++ program, is it correct for me to do this:

int i;
FILE **files = malloc(numFiles * sizeof(FILE *));
std::string file("foo"), ext(".bar");
char *num[10];

for (i = 0; i < numFiles; i++) {
    files[i] = fopen((file + itoa(i, num, 10) + ext).c_str(), "w");
}

This is basically what I am doing, but I am not getting anything written to the files. They're blank.

EDIT

I have fixed my problem. I thought I might be doing something wrong here, but it turned out to be elsewhere. Thanks for the responses, anyway.

Is it C or C++? If you're already using std::string, why not other C++ features instead of, say, raw arrays. — Qaz
– Qaz, Commented Aug 20, 2012 at 15:56
Well, there are no output operations in the code you've shown... — jrok
– jrok, Commented Aug 20, 2012 at 15:56
This is an apparently correct, if ugly, C++ (not C or C/C++) fragment. What do you expect it to do? — n. m. could be an AI
– n. m. could be an AI, Commented Aug 20, 2012 at 16:05
In my experience, C++ is ugly however you write it. I am not a huge fan. — Luke
– Luke, Commented Aug 20, 2012 at 16:27
@Luke: It's certainly ugly if you try to blend it with C idioms like that. In my opinion, it can be rather elegant (if occasionally somewhat twisted) if you stick to native idioms. — Mike Seymour
– Mike Seymour, Commented Aug 20, 2012 at 16:30

MLeblanc · Accepted Answer · 2012-08-20 15:59:07Z

4

Sure they are blanked, you did not write anything, you simply open the file in writing mode!

You have to use the fwrite or fprintf function to write the data to the file and then close the file with fclose.

answered Aug 20, 2012 at 15:59

MLeblanc

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8 Comments

elyashiv Over a year ago

or use ofstream and ofstream.operator<<() method.

jrok Over a year ago

If you're compiling C++, you need to cast the result of malloc (which is void*). And itoa is a non-standard function. Other than that, code seems ok.

fasked Over a year ago

@Luke, the initialization is correct if no error will happen. Do you use fclose function somewhere?

n. m. could be an AI Over a year ago

Show a self-contained complete program that demonstrates your problem.

Alex Reynolds Over a year ago

@elyashiv: Performance is one good reason not to use the C++ stream classes. The C equivalents are not as easy to set up and use, but they often work faster. This could be an important consideration, as reading and writing output streams is slow to begin with.

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fasked · Accepted Answer · 2012-08-20 16:10:31Z

2

You have array of pointers to char. But you need array of char. char *num[10]; --> char num[10].

I am wondering how it isn't crashing :)

answered Aug 20, 2012 at 16:10

fasked

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1 Comment

Luke Over a year ago

That was just a typo... it's not like that in the real program.

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