help regarding Struct in C

[gunner666]

Hi ,i want to know wat the : stands for, or does to the program here below

typedef struct ref
{
unsigned int en:1;
unsigned int sm:4;
unsigned int g:8;
unsigned int gate:16;
}
i want to know what does
en:1 really mean,
is it like assignin the variable en wid 1 ,or is it somethin else
plzzzzz reply

[gpraghuram]

Hi ,i want to know wat the : stands for, or does to the program here below

typedef struct ref
{
unsigned int en:1;
unsigned int sm:4;
unsigned int g:8;
unsigned int gate:16;
}
i want to know what does
en:1 really mean,
is it like assignin the variable en wid 1 ,or is it somethin else
plzzzzz reply

It is specifying how many bits you are going to use for storing the value.go through this link to get a good idea abt this

Raghuram

[krishnabhargav]

Hi ,i want to know wat the : stands for, or does to the program here below

typedef struct ref
{
unsigned int en:1;
unsigned int sm:4;
unsigned int g:8;
unsigned int gate:16;
}
i want to know what does
en:1 really mean,
is it like assignin the variable en wid 1 ,or is it somethin else
plzzzzz reply

Those are called Bit Fields...

en is 1 bit, sm is 4 bits and g is 8 bits while gate is 16 bits

refer : http://www.informit.co m/guides/content.aspx?g= cplusplus&seqNu m=131

[krishnabhargav]

Simple example to illustrate bitfields

#include<iostream>

using namespace std;

typedef struct ref
{
  unsigned int i:4;
  unsigned int j:2;
};

int main()
{
   ref r1;
   cout<<sizeof(r1)<<endl;
   r1.j = 3; //since r1 is 2 bits, max value is "11"(binary) or 3
   cout<<"Value of r1.j(2 bits)"<<r1.j<<endl;
   r1.j = 8; //100 in binary, cannot set 100, instead sets 00 to j's bits
   cout<<"Value of r1.j(2 bits)"<<r1.j<<endl;
}

[weaknessforcats]

You are using C++ where bit fields are supported as a deprecated feature only to compile relic C code. You are not supposed to use bit fields in new C++ code.

Use a bitset<>:
[code=cpp]
bitset<32> bits; //32 bits
[/code]