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Why cant I open a file by its explicit path?
Why can't I open a file by its explicit path? The call fopen("c:\newdir\file.dat", "r") is failing. The file you actually requested--with the characters \n and \f in its name--probably doesn't exist, and isn't what you thought you were trying to open. In character constants and string literals, the ... 2015-04-08, 1704👍, 0💬

What should malloc0 do? Return a null pointer or a pointer to 0 bytes?
What should malloc0 do? Return a null pointer or a pointer to 0 bytes? The ANSI/ISO Standard says that it may do either; the behavior is implementation-defined Portable code must either take care not to call malloc(0), or be prepared for the possibility of a null return. 2015-12-04, 1703👍, 0💬

What are the complete rules for header file searching?
What are the complete rules for header file searching? The exact behavior is implementation-defined (which means that it is supposed to be documented; Typically, headers named with &lt;> syntax are searched for in one or more standard places. Header files named with "" syntax are first searched ... 2016-02-12, 1699👍, 0💬

Why does the simple line-copying loop while ...
Why does the simple line-copying loop while(!feof(infp)) { fgets(buf, MAXLINE, infp); fputs(buf, outfp); } copy the last line twice? p> In C, end-of-file is only indicated after an input routine has tried to read, and failed. (In other words, C's I/O is not like Pascal's.) Usually, you should just c... 2015-11-13, 1697👍, 0💬

Why is my simple program, which hardly does more than print
Why is my simple program, which hardly does more than print ``Hello, world!'' in a window, compiling to such a huge executable (several hundred K)? Should I #include fewer header files? What you're seeing is the current (poor) state of the ``art'' in library design. As run-time libraries accrete mor... 2015-07-06, 1697👍, 0💬

Is it acceptable for one header file to #include another?
Is it acceptable for one header file to #include another? It's a question of style, and thus receives considerable debate. Many people believe that ``nested #include files'' are to be avoided: the prestigious Indian Hill Style Guide disparages them; they can make it harder to find relevant definitio... 2016-02-16, 1696👍, 0💬

What is assert and when would I use it?
What is assert and when would I use it? It is a macro, defined in &lt;assert.h>, for testing ``assertions''. An assertion essentially documents an assumption being made by the programmer, an assumption which, if violated, would indicate a serious programming error. For example, a function which ... 2015-01-12, 1696👍, 0💬

How can I clear the screen? How can I print text in color? How can I move the cursor to a specific x, y position?
How can I clear the screen? How can I print text in color? How can I move the cursor to a specific x, y position? Such things depend on the terminal type (or display) you're using. You will have to use a library such as termcap, terminfo, or curses, or some system-specific routines, to perform these... 2015-04-27, 1693👍, 0💬

Is C a great language, or what?
Is C a great language, or what? Where else could you write something like a+++++b ? A: Well, you can't meaningfully write it in C, either. The rule for lexical analysis is that at each point during a straightforward left-to-right scan, the longest possible token is determined, without regard to whet... 2015-01-26, 1691👍, 0💬

I a'm getting strange syntax errors inside lines I have ifdeffed out.
I a'm getting strange syntax errors inside lines I have ifdeffed out. Under ANSI C, the text inside a ``turned off'' #if, #ifdef, or #ifndef must still consist of ``valid preprocessing tokens.'' This means that the characters " and ' must each be paired just as in real C code, and the pairs mustn't ... 2016-01-29, 1690👍, 0💬

I am getting strange syntax errors inside lines I have ifdeffed out.
I am getting strange syntax errors inside lines I have ifdeffed out. Under ANSI C, the text inside a ``turned off'' #if, #ifdef, or #ifndef must still consist of ``valid preprocessing tokens.'' This means that the characters " and ' must each be paired just as in real C code, and the pairs mustn't c... 2015-12-14, 1689👍, 0💬

How can I recover the file name given an open stream or file descriptor?
How can I recover the file name given an open stream or file descriptor? 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 r... 2015-04-10, 1689👍, 0💬

My ANSI compiler complains about a mismatch when it see
My ANSI compiler complains about a mismatch when it sees extern int func(float); int func(x) float x; { ... You have mixed the new-style prototype declaration ``extern int func(float);'' with the old-style definition ``int func(x) float x;''. It is usually possible to mix the two styles but not in t... 2016-01-13, 1688👍, 0💬

I am splitting up a program into multiple source files for the first time ...
I'm splitting up a program into multiple source files for the first time, and I'm wondering what to put in .c files and what to put in .h files. (What does ``.h'' mean, anyway?) As a general rule, you should put these things in header (.h) files: macro definitions (preprocessor #defines) structure, ... 2016-02-18, 1686👍, 0💬

How can I discover how many arguments a function was actually called with?
How can I discover how many arguments a function was actually called with? This information is not available to a portable program. Some old systems provided a nonstandard nargs function, but its use was always questionable, since it typically returned the number of words passed, not the number of a... 2015-06-10, 1683👍, 0💬

Is there a way to switch on strings?
Is there a way to switch on strings? Not directly. Sometimes, it's appropriate to use a separate function to map strings to integer codes, and then switch on those: #define CODE_APPLE 1 #define CODE_ORANGE 2 #define CODE_NONE 0 switch(classifyfunc(string)) { case CODE_APPLE: ... case CODE_ORANGE: ..... 2015-02-04, 1683👍, 0💬

Are the outer parentheses in return statements really optional?
Are the outer parentheses in return statements really optional? Yes. Long ago, in the early days of C, they were required, and just enough people learned C then, and wrote code which is still in circulation, that the notion that they might still be required is widespread. (As it happens, parentheses... 2015-02-02, 1683👍, 0💬

How can I find out how much memory is available?
How can I find out how much memory is available? Your operating system may provide a routine which returns this information, but it's quite system-dependent. (Also, the number may vary over time.) If you're trying to predict whether you'll be able to allocate a certain amount of memory, just try it-... 2015-03-30, 1682👍, 0💬

How can I find the day of the week given the date?
How can I find the day of the week given the date? Here are three methods: 1. Use mktime or localtime # . Here is a code fragment which computes the day of the week for February 29, 2000: #include &lt;stdio.h> #include &lt;time.h> char *wday[] = {"Sunday", "Monday", "Tuesday", "Wednesday", "... 2015-01-07, 1682👍, 0💬

fopen isnt letting me open files like "$HOME/.profile" and "~/.myrcfile".
fopen isn't letting me open files like "$HOME/.profile" and "~/.myrcfile". Under Unix, at least, environment variables like $HOME, along with the home-directory notation involving the ~ character, are expanded by the shell, and there's no mechanism to perform these expansions automatically when you ... 2015-04-06, 1681👍, 0💬

What if a built-in logical or relational operator `returns something other than 1? ....
Isn't #defining TRUE to be 1 dangerous, since any nonzero value is considered ``true'' in C? What if a built-in logical or relational operator ``returns'' something other than 1? It is true (sic) that any nonzero value is considered true in C, but this applies only ``on input'', i.e. where a Boolean... 2016-02-29, 1678👍, 0💬

Can I use base-2 constants (something like 0b101010)? Is there a printf format for binary?
Can I use base-2 constants (something like 0b101010)? Is there a printf format for binary? No, on both counts, although there are various preprocessor tricks you can try. You can convert base-2 string representations to integers with strtol. If you need to print numbers out in base 2, . 2015-02-13, 1677👍, 0💬

How can I sort a linked list?
How can I sort a linked list? Sometimes it's easier to keep the list in order as you build it (or perhaps to use a tree instead). Algorithms like insertion sort and merge sort lend themselves ideally to use with linked lists. If you want to use a standard library function, you can allocate a tempora... 2015-08-10, 1673👍, 0💬

How can I call system when parameters (filenames, etc.) of the executed command arent known until run time?
How can I call system when parameters (filenames, etc.) of the executed command arent known until run time? Just use sprintf (or perhaps strcpy and strcat) to build the command string in a buffer, then call system with that buffer. (Make sure the buffer is allocated with enough space; Here is a cont... 2015-03-18, 1673👍, 0💬

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.NET C C++ CSS DBA General HTML Java JavaScript JSP JUnit MySQL Networking Oracle Perl Perl PHP PL/SQL RSS Software QA SQL Server Struts Unix Windows XHTML XML