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C

05/20/19

Why do you have to link the math library in C?

If I include `<stdlib.h>` or `<stdio.h>` in a C program I don't have to link these when compiling but I do have to link to `<math.h>`, using `-lm` with gcc, for example: gcc... more

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C

05/20/19

How to initialize all members of an array to the same value?

I have a large array in C (not C++ if that makes a difference). I want to initialize all members to the same value. I could swear I once knew a simple way to do this. I could use `memset()` in my... more

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C

05/20/19

How do I concatenate const/literal strings in C?

I'm working in C, and I have to concatenate a few things.Right now I have this: message = strcat("TEXT ", var); message2 = strcat(strcat("TEXT ", foo), strcat(" TEXT ", bar));Now if you have... more

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C

05/20/19

What REALLY happens when you don't free after malloc?

This has been something that has bothered me for ages now.We are all taught in school (at least, I was) that you MUST free every pointer that is allocated. I'm a bit curious, though, about the... more

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C

05/20/19

Why does printf not flush after the call unless a newline is in the format string?

Why does `printf` not flush after the call unless a newline is in the format string? Is this POSIX behavior? How might I have `printf` immediately flush every time?

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C

05/20/19

Is an array name a pointer?

Is an array's name a pointer in C?If not, what is the difference between an array's name and a pointer variable?

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C

05/19/19

Pointers in C: when to use the ampersand and the asterisk?

I'm just starting out with pointers, and I'm slightly confused. I know `&` means the address of a variable and that `*` can be used in front of a pointer variable to get the value of the object... more

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C

05/19/19

Most Efficient Algorithm for Bit Reversal ( from MSB->LSB to LSB->MSB) in C?

What is the best algorithm to achieve the following:`0010 0000 => 0000 0100`The conversion is from MSB->LSB to LSB->MSB. All bits must be reversed; that is, this is *not*... more

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C

05/19/19

How to make a variadic macro (variable number of arguments)?

I want to write a macro in C that accepts any number of parameters, not a specific numberexample: #define macro( X ) something_complicated( whatever( X ) )where `X` is any number of parametersI... more

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C

05/19/19

Why does the arrow (->) operator in C exist?

The dot (`.`) operator is used to access a member of a struct, while the arrow operator (`->`) in C is used to access a member of a struct which is referenced by the pointer in question.The... more

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C

05/19/19

How to define an enumerated type (enum) in C?

I'm not sure what is the proper syntax for using C enums. I have the following code: enum {RANDOM, IMMEDIATE, SEARCH} strategy; strategy = IMMEDIATE;But this does not compile, with the... more

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C

05/18/19

Forward an invocation of a variadic function in C?

In C, is it possible to forward the invocation of a variadic function? As in, int my_printf(char *fmt, ...) { fprintf(stderr, "Calling printf with fmt %s", fmt); return... more

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C

05/18/19

How to expand nested variables in makefile?

I am using simulink to generate c-code. For the compilation of the code a generate makefile is used. In this make file the following variable "MAKECMD" is made. This variable is used to make a... more

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C

05/18/19

How do I use extern to share variables between source files?

I know that global variables in C sometimes have the `extern` keyword. What is an `extern` variable? What is the declaration like? What is its scope?This is related to sharing variables across... more

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C

05/17/19

Arrow operator (->) usage in C?

I am currently learning C by reading a good beginner's book called "Teach Yourself C in 21 Days" (I have already learned Java and C# so I am moving at a much faster pace). I was reading the chapter... more

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C

05/15/19

Why use double pointer? or Why use pointers to pointers?

When should a double pointer be used in C? Can anyone explain with a example?What I know is that a double pointer is a pointer to a pointer. Why would I need a pointer to a pointer?

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C Linux Unix File Io

05/14/19

C fopen vs open?

Is there any reason (other than syntactic ones) that you'd want to use FILE *fdopen(int fd, const char *mode);or FILE *fopen(const char *path, const char *mode);instead of int open(const... more

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C Unix Segmentation Fault Bus Error

05/11/19

What is a bus error?

What does the "bus error" message mean, and how does it differ from a segfault?

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C Photography Algorithm Light

05/11/19

How to convert between lux and exposure value?

How to convert from an [exposure value][1] to [lux][2]? Thanks! i.e. what's the formula behind [this chart][3]? [1]:... more

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C

05/10/19

What is the >>>= operator in C?

Given by a colleague as a puzzle, I cannot figure out how this C program actually compiles and runs. What is this `>>>=` operator and the strange `1P1` literal? I have tested in Clang and... more

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C

05/10/19

Effects of the extern keyword on C functions?

In C, I did not notice any effect of the `extern` keyword used before function declaration.At first, I thought that when defining `extern int f();` in a single file **forces** you to implement it... more

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C

05/08/19

size_t vs. uintptr_t?

The C standard guarantees that `size_t` is a type that can hold any array index. This means that, logically, `size_t` should be able to hold any pointer type. I've read on some sites that I found... more

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C

05/08/19

How to correctly use the extern keyword in C?

My question is about when a function should be referenced with the `extern` keyword in C.I am failing to see when this should be used in practice. As I am writing a program all of the functions... more

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C

05/08/19

register keyword in C?

What does the `register` keyword do in C language? I have read that it is used for optimizing but is not clearly defined in any standard. Is it still relevant and if so, when would you use it?

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C

05/07/19

Divide a number by 3 without using *, /, +, -, % operators?

How would you divide a number by 3 without using `*`, `/`, `+`, `-`, `%`, operators?The number may be signed or unsigned.

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Why do you have to link the math library in C?

How to initialize all members of an array to the same value?

How do I concatenate const/literal strings in C?

What REALLY happens when you don't free after malloc?

Why does printf not flush after the call unless a newline is in the format string?

Is an array name a pointer?

Pointers in C: when to use the ampersand and the asterisk?

Most Efficient Algorithm for Bit Reversal ( from MSB->LSB to LSB->MSB) in C?

How to make a variadic macro (variable number of arguments)?

Why does the arrow (->) operator in C exist?

How to define an enumerated type (enum) in C?

Forward an invocation of a variadic function in C?

How to expand nested variables in makefile?

How do I use extern to share variables between source files?

Arrow operator (->) usage in C?

Why use double pointer? or Why use pointers to pointers?

C fopen vs open?

What is a bus error?

How to convert between lux and exposure value?

What is the >>>= operator in C?

Effects of the extern keyword on C functions?

size_t vs. uintptr_t?

How to correctly use the extern keyword in C?

register keyword in C?

Divide a number by 3 without using *, /, +, -, % operators?

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