storage-class-specifier

Do the C language standards specify support for global register variables

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问题 I read that gcc provides support to define global variables as register stored variables. What I want to know is that do the standards have any specifications for this support. 回答1: There is a common misconsception that C's keyword register talks about hardware registers. That might be the origin of that concept, but in modern C this is not the purpose. The only real effect that register has, is that the & is not allowed on such a beast. They may be realized in any way the compiler wants,

Why can't I specify the storage class for formal parameters of a function?

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问题 When I do as below the code works fine : #include <stdio.h> void test( int a) { printf("a=%d\n",a); } int main() { test(10); return 1; } But when I do #include <stdio.h> void test( auto int a) // Or static int a Or extern int a { printf("a=%d\n",a); } int main() { test(10); return 1; } It generates an error, error: storage class specified for parameter 'a' Why is that error? What happens internally(memory management)? But it works fine without any error when I do: void test( register int a) {

What is the difference between “File scope” and “program scope”

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问题 A variable declared globally is said to having program scope A variable declared globally with static keyword is said to have file scope. For example: int x = 0; // **program scope** static int y = 0; // **file scope** static float z = 0.0; // **file scope** int main() { int i; /* block scope */ /* . . . */ return 0; } What is the difference between these two? 回答1: In C99, there's nothing called "program scope". In your example variable x has a file scope which terminates at the end of

Can a variable be declared both static and extern?

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问题 Why the following doesn't compile? ... extern int i; static int i; ... but if you reverse the order, it compiles fine. ... static int i; extern int i; ... What is going on here? 回答1: This is specifically given as an example in the C++ standard when it's discussing the intricacies of declaring external or internal linkage. It's in section 7.1.1.7, which has this exert: static int b ; // b has internal linkage extern int b ; // b still has internal linkage extern int d ; // d has external

How many registers are used when a variable is declared using register storage class?

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问题 My question is simply, how many registers will a C compiler use for a variable declared using register storage class as : register int a . I have read this answer How many register and what kind of register are available for the storage class REGISTER in c language but could not understand much. I know it can be implementation dependent, but then this registers are limited, so when would the compiler ignore the declaration or will it generate an error? 回答1: C11 still supports register : A

Impact of the type qualifiers on storage locations

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问题 As mentioned in the title, I am little confused if the type-qualifiers impact the storage location ( stack , bss etc..) of the declarator.To describe more I am considering the following declarations. int main() { const int value=5; const char *str= "Constant String"; } In the above code, the default storage-class-specifier is auto . Hence it is assumed that these constants will be allocated in the stack-frame of main when it is created. Generally, the pointers to various memory locations in

What does it mean to declare a variable with a storage class specifier but no type specifier?

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问题 After reading through the ANSI C Yacc grammar specification I noticed the following are all valid: register x; auto y; static z; extern q; This seems strange to me, as my understanding of type would suggest that none of these variables have a type. What do these mean? How are they type checked? How much memory is allocated? 回答1: Before C99 if a type was not specified it defaulted to int this was supposed to be removed in C99 but many compilers support it even in C99 mode. For example in clang

How many register and what kind of register are available for the storage class REGISTER in c language

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问题 Register storage class is used to quicky access the variable and its memory is allocated in CPU. But the registers in the cpu are limited. I use an intel Core i5-4260U Processor. I've visited intel website for the details of the register. But I couldn't find any of such specification of how many registers does the cpu contain (to visit website click here). Even if i could find that the number of registers((from How many registers are there in 8086/8088?)) but I couldn't figure out how many of

How many register and what kind of register are available for the storage class REGISTER in c language

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Register storage class is used to quicky access the variable and its memory is allocated in CPU. But the registers in the cpu are limited. I use an intel Core i5-4260U Processor. I've visited intel website for the details of the register. But I couldn't find any of such specification of how many registers does the cpu contain (to visit website click here ). Even if i could find that the number of registers((from How many registers are there in 8086/8088? )) but I couldn't figure out how many of these are used by c storage classes. But I couldn't find any of such specification of how many

Why BSS segment is “16” by default?

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问题 As per my knowledge, segmentation for c program is: High address |---------------------------| |env/cmd line args vars | |---------------------------| | stack segment |--> uninitialized auto vars |---------------------------| |---------------------------| |---------------------------| | heap segment |--> dynamic allocated memory |---------------------------| | BSS segment |--> uninitialized static/global vars |---------------------------| | data segment |--> initialized static/global vars |--