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Why cant I pass a char to a function which expects a const char ?
Why cant I pass a char to a function which expects a const char ? You can use a pointer-to-T (for any type T) where a pointer-to-const-T is expected. However, the rule (an explicit exception) which permits slight mismatches in qualified pointer types is not applied recursively, but only at the top l... 2016-01-04, 1036👍, 0💬

Why doesnt strcat work? ....
Why doesn't strcat(string, '!'); work? There is a very real difference between characters and strings, and strcat concatenates strings. A character constant like '!' represents a single character. A string literal between double quotes usually represents multiple characters. A string literal like "!... 2016-03-14, 1035👍, 0💬

My programs prompts and intermediate output dont always show up on the screen ...
My program's prompts and intermediate output don't always show up on the screen, especially when I pipe the output through another program. It's best to use an explicit fflush(stdout) whenever output should definitely be visible (and especially if the text does not end with \n). Several mechanisms a... 2015-11-11, 1035👍, 0💬

How can I tell how much destination buffer space ...
How can I tell how much destination buffer space I'll need for an arbitrary sprintf call? How can I avoid overflowing the destination buffer with sprintf? When the format string being used with sprintf is known and relatively simple, you can sometimes predict a buffer size in an ad-hoc way. If the f... 2015-10-19, 1035👍, 0💬

How can I find the modification date and time of a file?
How can I find the modification date and time of a file? The Unix and POSIX function is stat, which several other systems supply as well. 2015-04-13, 1035👍, 0💬

I mm compiling a program, and I seem to be missing one of the header files it requires
I mm compiling a program, and I seem to be missing one of the header files it requires There are several situations, depending on what sort of header file it is that's ``missing''. If the missing header file is truly a standard one (that is, one defined by the ANSI C Standard, such as &lt;stdio.... 2016-02-05, 1034👍, 0💬

How can I write a macro which takes a variable number of arguments ....
How can I write a macro which takes a variable number of arguments, or use the preprocessor to ``turn off'' a function call with a variable number of arguments? One popular trick is to define and invoke the macro with a single, parenthesized ``argument'' which in the macro expansion becomes the enti... 2016-01-19, 1033👍, 0💬

I am having trouble with a Turbo C program which crashes
I'm having trouble with a Turbo C program which crashes and says something like ``floating point formats not linked.'' Some compilers for small machines, including Turbo C (and Ritchie's original PDP-11 compiler), leave out certain floating point support if it looks like it will not be needed. In pa... 2015-06-19, 1033👍, 0💬

How can I write a function that takes a format string and a variable number of arguments
How can I write a function that takes a format string and a variable number of arguments, like printf, and passes them to printf to do most of the work? Use vprintf, vfprintf, or vsprintf. These routines are like their counterparts printf, fprintf, and sprintf, except that instead of a variable-leng... 2015-06-12, 1033👍, 0💬

How can I find out the size of a file, prior to reading it in?
How can I find out the size of a file, prior to reading it in? If the ``size of a file'' is the number of characters you'll be able to read from it in C (or which were written to it by a previous program), it can be difficult or impossible to determine this number exactly (other than by reading the ... 2015-04-15, 1033👍, 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, 1032👍, 0💬

What does pragma once mean? I found it in some header files.
What does pragma once mean? I found it in some header files. It is an extension implemented by some preprocessors to help make header files idempotent; that is, to make sure that their contents are processed exactly once even if they are #included multiple times.Some people claim that #pragma once c... 2015-12-11, 1032👍, 0💬

I had a frustrating problem which turned out to be caused by the line
I had a frustrating problem which turned out to be caused by the line printf("%d", n); where n was actually a long int. I thought that ANSI function prototypes were supposed to guard against argument type mismatches like this. When a function accepts a variable number of arguments, its prototype doe... 2015-06-15, 1031👍, 0💬

What is the best style for code layout in C?
What is the best style for code layout in C? While providing the example most often copied, also supply a good excuse for disregarding it: The position of braces is less important, although people hold passionate beliefs. We have chosen one of several popular styles. Pick a style that suits you, the... 2015-05-18, 1031👍, 0💬

How can I use a preprocessorif expression to ? ....
How can I use a preprocessor #if expression to tell whether a machine's byte order is big-endian or little-endian? You probably can't. The usual techniques for detecting endianness involve pointers or arrays of char, or maybe unions, but preprocessor arithmetic uses only long integers, and there is ... 2016-02-01, 1028👍, 0💬

Why do all the lines end up containing copies of the last line?
I'm using fgets to read lines from a file into an array of pointers. Why do all the lines end up containing copies of the last line? You have only allocated memory for one line, linebuf. Each time you call fgets, the previous line is overwritten. fgets doesn't do any memory allocation: unless it rea... 2015-11-13, 1028👍, 0💬

My compiler is complaining that printf is undefined ...
My compiler is complaining that printf is undefined! How can this be? It's the world's most popular C function... Allegedly, there are C compilers for Microsoft Windows which do n ot support printf, on the argument that printf is for printing to old-fashioned terminals, while under Windows the right... 2015-07-03, 1028👍, 0💬

Why do some people write if(0 == x) instead of if(x == 0)?
Why do some people write if(0 == x) instead of if(x == 0)? It's a trick to guard against the common error of writing if(x = 0) If you're in the habit of writing the constant before the ==, the compiler will complain if you accidentally type if(0 = x) Evidently it can be easier for some people to rem... 2015-05-15, 1028👍, 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, 1027👍, 0💬

What does it mean when the linker says that _end is undefined?
What does it mean when the linker says that _end is undefined? That message is a quirk of the old Unix linkers. You get an error about _end being undefined only when other symbols are undefined, too--fix the others, and the error about _end will disappear. 2015-07-06, 1027👍, 0💬

How can I get random integers in a certain range?
How can I get random integers in a certain range? The obvious way, rand() % N /* POOR */ (which tries to return numbers from 0 to N-1) is poor, because the low-order bits of many random number generators are distressingly non-random. A better method is something like (int)((double)rand() / ((double)... 2015-07-29, 1026👍, 0💬

I have a pre-ANSI compiler, without stdarg.h What can I do?
I have a pre-ANSI compiler, without stdarg.h What can I do? There's an older header, &lt;varargs.h>, which offers about the same functionality. Here is the vstrcat function, rewritten to use &lt;varargs.h>: #include &lt;stdio.h> #include &lt;varargs.h> #include &lt;string.h> exte... 2015-06-10, 1026👍, 0💬

I have a program that seems to run correctly
I have a program that seems to run correctly, but it crashes as it's exiting, after the last statement in main(). What could be causing this? A:There are at least three things to look for: 1. If a semicolon in a previous declaration is missing, main might be inadvertently declared as returning a str... 2015-05-29, 1026👍, 0💬

I am getting baffling syntax errors which make no sense at all
I'm getting baffling syntax errors which make no sense at all, and it seems like large chunks of my program aren't being compiled. Check for unclosed comments, mismatched #if/#ifdef/#ifndef/#else/#endi fdirectives, and perhaps unclosed quotes; remember to check header files, too. 2015-06-01, 1024👍, 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