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Does C have anything like the `substr extract substrin routine present in other languages?
Does C have anything like the `substr extract substrin routine present in other languages? Not as such. To extract a substring of length LEN starting at index POS in a source string, use something like char dest[LEN+1]; strncpy(dest, &source[POS], LEN); dest[LEN] = '\0'; /* ensure \0 termination */ ...
2016-03-07, 324👍, 0💬

I am reading strings typed by the user into an array ...
I'm reading strings typed by the user into an array, and then printing them out later. When the user types a sequence like \n, why isn't it being handled properly? Character sequences like \n are interpreted at compile time. When a backslash and an adjacent n appear in a character constant or string...
2016-03-04, 359👍, 0💬

I think somethings wrong with my compiler ...
I think something's wrong with my compiler: I just noticed that sizeof('a') is 2, not 1 (i.e. not sizeof(char)). Perhaps surprisingly, character constants in C are of type int, so sizeof('a') is sizeof(int) (though this is another area where C++ differs).
2016-03-04, 343👍, 0💬

I am starting to think about multinational character sets ....
I'm starting to think about multinational character sets, and I'm worried about the implications of making sizeof(char) be 2 so that 16-bit character sets can be represented. If type char were made 16 bits, sizeof(char) would still be 1, and CHAR_BIT in <limits.h> would be 16, and it would simply...
2016-03-02, 317👍, 0💬

What is the right type to use for Boolean values in C? ....
What is the right type to use for Boolean values in C? Is there a standard type? Should I use #defines or enums for the true and false values? Traditionally, C did not provide a standard Boolean type, partly and partly to allow the programmer to make the appropriate space/time tradeoff. (Using an in...
2016-03-02, 333👍, 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, 312👍, 0💬

Is if(p), where p is a pointer, a valid and portable test?
Is if(p), where p is a pointer, a valid and portable test? It is always valid. When C requires the Boolean value of an expression, a false value is inferred when the expression compares equal to zero, and a true value otherwise. That is, whenever one writes if(expr) where ``expr'' is any expression ...
2016-02-29, 313👍, 0💬

Should I use symbolic names like TRUE and FALSE for Boolean constants, or plain 1 and 0?
Should I use symbolic names like TRUE and FALSE for Boolean constants, or plain 1 and 0? It's your choice. Preprocessor macros like TRUE and FALSE (and, of course, NULL) are used for code readability, not because the underlying values might ever change. It's a matter of style, not correctness, wheth...
2016-02-29, 342👍, 0💬

A third-party header file I just started using is defining its own TRUE and FALSE values incompatibly ...
A third-party header file I just started using is defining its own TRUE and FALSE values incompatibly with the code I've already developed. What can I do? This is indeed an annoying situation. It's a classic namespace problem;Ideally, third-party vendors would be conscientious when defining symbols ...
2016-02-26, 331👍, 0💬

I am trying to define a few simple little function-like macros ...
I'm trying to define a few simple little function-like macros such as #define square(x) x * x but they're not always working. There are three important rules to remember when defining function-like macros: 1. The macro expansion must always be parenthesized to protect any lower-precedence operators ...
2016-02-26, 335👍, 0💬

I can write C code that looks more like Pascal? ....
Here are some cute preprocessor macros: #define begin { #define end } With these, I can write C code that looks more like Pascal. What do y'all think? Use of macros like these, though perhaps superficially attractive, is generally discouraged; in severe cases the practice is called ``preprocessor ab...
2016-02-24, 332👍, 0💬

How can I write a generic macro to swap two values?
How can I write a generic macro to swap two values? There is no good answer to this question. If the values are integers, a well-known trick using exclusive-OR could perhaps be used, but it will not work for floating-point values or pointers, or if the two values are the same variable. If the macro ...
2016-02-24, 342👍, 0💬

What's the best way to write a multi-statement macro?
What's the best way to write a multi-statement macro? The usual goal is to be able to invoke the macro as if it were an expression statement consisting of a function call: MACRO(arg1, arg2); This means that the ``caller'' will be supplying the final semicolon, so the macro body should not. The macro...
2016-02-22, 658👍, 0💬

What's the difference between using a typedef or a define for a user-defined type?
What's the difference between using a typedef or a define for a user-defined type? In general, typedefs are preferred, in part because they can correctly encode pointer types. For example, consider these declarations: typedef char *String_t; #define String_d char * String_t s1, s2; String_d s3, s4; ...
2016-02-22, 337👍, 0💬

What is the difference between ...
What's the difference between const MAXSIZE = 100; and #define MAXSIZE 100 A preprocessor #define gives you a true compile-time constant. In C, const gives you a run-time object which you're not supposed to try to modify; ``const'' really means ``readonly''.
2016-02-18, 325👍, 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, 319👍, 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, 365👍, 0💬

What's the difference between...?
What's the difference between #include <> and #include "" ? The syntax is typically used with Standard or system-supplied headers, while "" is typically used for a program's own header files.
2016-02-16, 342👍, 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 <> syntax are searched for in one or more standard places. Header files named with "" syntax are first searched for ...
2016-02-12, 340👍, 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, 317👍, 0💬

I am using header files which accompany two different third-party libraries...
I'm using header files which accompany two different third-party libraries, and they are ``helpfully'' defining common macros such as TRUE, FALSE, Min(), and Max(), but the definitions clash with each other and with definitions I'd already established in my own header files. What can I do? This is i...
2016-02-10, 347👍, 0💬

I am including the right header file for the library function I am using, but the linker keeps saying its undefined.
I am including the right header file for the library function I am using, but the linker keeps saying its undefined. In the general case of calling code in an external library, using #include to pull in the right header file(s) is only half of the story; you also have to tell the linker to search th...
2016-02-10, 358👍, 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 <stdio.h>),...
2016-02-05, 358👍, 0💬

How can I construct preprocessor if expressions which compare strings?
How can I construct preprocessor if expressions which compare strings? You can't do it directly; preprocessor #if arithmetic uses only integers. An alternative is to #define several macros with symbolic names and distinct integer values, and implement conditionals on those: #define RED 1 #define BLU...
2016-02-05, 347👍, 0💬

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