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How can I sort more data than will fit in memory?
How can I sort more data than will fit in memory? You want an ``external sort,'' which you can read about in Knuth, Volume 3. The basic idea is to sort the data in chunks (as much as will fit in memory at one time), write each sorted chunk to a temporary file, and then merge the files. Your operatin...
2015-08-07, 1351👍, 0💬

How should functions be apportioned among source files?
How should functions be apportioned among source files? Usually, related functions are put together in one file. Sometimes (as when developing libraries) it is appropriate to have exactly one source file (and, consequently, one object module) per independent function. Other times, and especially for...
2015-05-18, 1347👍, 0💬

How can I arrange to have output go two places at once, e.g. to the screen and to a file?
How can I arrange to have output go two places at once, e.g. to the screen and to a file? You can't do this directly, but you could write your own printf variant which printed everything twice. Here is a sample logprintf function which prints to both stdout and a preopened log file: #include &lt...
2015-09-29, 1346👍, 0💬

How can I get back to the interactive keyboard if stdin is redirected?
I'm trying to write a program like ``more.'' How can I get back to the interactive keyboard if stdin is redirected? There is no portable way of doing this. Under Unix, you can open the special file /dev/tty. Under MS-DOS, you can try opening the ``file'' CON, or use routines or BIOS calls such as ge...
2015-09-29, 1341👍, 0💬

How can I write a function analogous to scanf
How can I write a function analogous to scanf, i.e. that accepts similar arguments, and calls scanf to do most of the work? C99 (but not any earlier C Standard) supports vscanf, vfscanf, and vsscanf.
2015-06-12, 1341👍, 0💬

How can I recover the file name given an open stream?
How can I recover the file name given an open stream? This problem is, in general, insoluble. Under Unix, for instance, a scan of the entire disk (perhaps involving special permissions) would theoretically be required, and would fail if the descriptor were connected to a pipe or referred to a delete...
2015-10-05, 1337👍, 0💬

I am getting strange syntax errors on the very first declaration in a file, but it looks fine.
I am getting strange syntax errors on the very first declaration in a file, but it looks fine. Perhaps there's a missing semicolon at the end of the last declaration in the last header file you're #including.
2016-02-12, 1333👍, 0💬

I am trying to port this old program. Why do I get undefined external errors for some library functions?
I am trying to port this old program. Why do I get undefined external errors for some library functions? Some old or semistandard functions have been renamed or replaced over the years; if you need:/you should instead: index use strchr. rindex use strrchr. bcopy use memmove, after interchanging the ...
2015-07-16, 1318👍, 0💬

How can I delete a file?
How can I delete a file? The Standard C Library function is remove. (This is therefore one of the few questions in this section for which the answer is not ``It's system-dependent.'') On older, pre-ANSI Unix systems, remove may not exist, in which case you can try unlink.
2015-04-10, 1307👍, 0💬

I wrote this routine which is supposed to open a fi
I wrote this routine which is supposed to open a file: myfopen(char *filename, FILE *fp) { fp = fopen(filename, "r"); } But when I call it like this: FILE *infp; myfopen("filename.dat", infp); the infp variable in the caller doesn't get set properly. Functions in C always receive copies of their arg...
2015-10-09, 1270👍, 0💬

I want to read and write numbers between files and memory ...
I want to read and write numbers between files and memory in a byte-at-a-time way, not as formatted characters the way fprintf and fscanf do. How can I do this? What you're trying to do is usually called ``binary'' I/O. First, make sure that you are calling fopen with the "b" modifier ("rb", "wb", e...
2015-09-24, 1195👍, 0💬

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