Ethereum Sign up or log in to customize your list._ Here's how it works: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top up vote 8 down vote favorite 1 I have a struct like so : struct fooStruct { uint foo; uint figther; } I would like to initialize that struct but it won't be stored in a mapping but inside an array.Is there a way to initialize the struct like fooStruct myStruct = fooStruct.new(par1,2,3) solidity contract-development struct up vote 8 down vote Yes, just use fooStruct myStruct = fooStruct(1,2); Or fooStruct myStruct = fooStruct({foo:1, fighter:2}); Or fooStruct memory myStruct; // for temporary data myStruct.figther = 2; // will only write to memory fooStruct storage myStruct = ...; // for persistent data, has to be initialized from a state variable.`storage` is the default and thus optional myStruct.fighter = 2; // will write directly to storage See the docs for more examples Your Answer Sign up or log in Sign up using Google Sign up using Email and Password Post as a guest Name Email discard By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged solidity contract-development struct or ask your own question.Solidity is a statically typed language, which means that the type of each variable (state and local) needs to be specified (or at least known - see below) at compile-time.Solidity provides several elementary types which can be combined to form complex types.In addition, types can interact with each other in expressions containing operators.For a quick reference of the various operators, see .Value Types The following types are also called value types because variables of these types will always be passed by value, i.e.they are always copied when they are used as function arguments or in assignments.Booleans : The possible values are constants and .(logical negation) (logical conjunction, “and”) (logical disjunction, “or”) (equality) (inequality) The operators and apply the common short-circuiting rules.This means that in the expression , if evaluates to , will not be evaluated even if it may have side-effects.

Integers / : Signed and unsigned integers of various sizes.Keywords to in steps of 8 (unsigned of 8 up to 256 bits) and to .bitcoin exchange mountand are aliases for and , respectively.bitcoin unstoppableOperators: Comparisons: , <, , , , > (evaluate to ) Bit operators: &, |, ^ (bitwise exclusive or), ~ (bitwise negation) Arithmetic operators: +, -, unary -, unary +, *, /, % (remainder), (exponentiation), (left shift), (right shift) Division always truncates (it just is compiled to the DIV opcode of the EVM), but it does not truncate if both operators are (or literal expressions).bitcoin exchange money launderingDivision by zero and modulus with zero throws a runtime exception.bitcoin linux miner

The result of a shift operation is the type of the left operand.The expression x y is equivalent to x * and x y is equivalent to x / .bitcoin millionaire app storeThis means that shifting negative numbers sign extends.btw op bitcoinsShifting by a negative amount throws a runtime exception.Warning The results produced by shift right of negative values of signed integer types is different from those produced by other programming languages.In Solidity, shift right maps to division so the shifted negative values are going to be rounded towards zero (truncated).In other programming languages the shift right of negative values works like division with rounding down (towards negative infinity).Address : Holds a 20 byte value (size of an Ethereum address).Address types also have members and serve as base for all contracts.

Operators: , <, , , and > Members of Addresses and For a quick reference, see .It is possible to query the balance of an address using the property and to send Ether (in units of wei) to an address using the function: x = ; = ; (x.Note If x is a contract address, its code (more specifically: its fallback function, if present) will be executed together with the call (this is a limitation of the EVM and cannot be prevented).If that execution runs out of gas or fails in any way, the Ether transfer will be reverted and the current contract will stop with an exception.Send is the low-level counterpart of .If the execution fails, the current contract will not stop with an exception, but will return .Warning There are some dangers in using : The transfer fails if the call stack depth is at 1024 (this can always be forced by the caller) and it also fails if the recipient runs out of gas.So in order to make safe Ether transfers, always check the return value of , use or even better: use a pattern where the recipient withdraws the money.

, and Furthermore, to interface with contracts that do not adhere to the ABI, the function is provided which takes an arbitrary number of arguments of any type.These arguments are padded to 32 bytes and concatenated.One exception is the case where the first argument is encoded to exactly four bytes.In this case, it is not padded to allow the use of function signatures here.a returns a boolean indicating whether the invoked function terminated () or caused an EVM exception ().It is not possible to access the actual data returned (for this we would need to know the encoding and size in advance).In a similar way, the function can be used: The difference is that only the code of the given address is used, all other aspects (storage, balance, ...)are taken from the current contract.The purpose of is to use library code which is stored in another contract.The user has to ensure that the layout of storage in both contracts is suitable for delegatecall to be used.Prior to homestead, only a limited variant called was available that did not provide access to the original and values.

All three functions , and are very low-level functions and should only be used as a last resort as they break the type-safety of Solidity.The option is available on all three methods, while the option is not supported for .Note All contracts inherit the members of address, so it is possible to query the balance of the current contract using .Warning All these functions are low-level functions and should be used with care.Specifically, any unknown contract might be malicious and if you call it, you hand over control to that contract which could in turn call back into your contract, so be prepared for changes to your state variables when the call returns.Fixed-size byte arrays , , , ..., .is an alias for .Operators: Comparisons: , <, , , , > (evaluate to ) Bit operators: &, |, ^ (bitwise exclusive or), ~ (bitwise negation), (left shift), (right shift) Index access: If x is of type , then for 0 k < I returns the k th byte (read-only).The shifting operator works with any integer type as right operand (but will return the type of the left operand), which denotes the number of bits to shift by.

Shifting by a negative amount will cause a runtime exception.Members: yields the fixed length of the byte array (read-only).Dynamically-sized byte array : Dynamically-sized byte array, see .: Dynamically-sized UTF-8-encoded string, see .As a rule of thumb, use for arbitrary-length raw byte data and for arbitrary-length string (UTF-8) data.If you can limit the length to a certain number of bytes, always use one of to because they are much cheaper.Fixed Point Numbers COMING SOON... Address Literals Hexadecimal literals that pass the address checksum test, for example are of type.Hexadecimal literals that are between 39 and 41 digits long and do not pass the checksum test produce a warning and are treated as regular rational number literals.Rational and Integer Literals Integer literals are formed from a sequence of numbers in the range 0-9.They are interpreted as decimals.For example, means sixty nine.Octal literals do not exist in Solidity and leading zeros are invalid.

Decimal fraction literals are formed by a .with at least one number on one side.Examples include , and .Scientific notation is also supported, where the base can have fractions, while the exponent cannot.Examples include , , , .Number literal expressions retain arbitrary precision until they are converted to a non-literal type (i.e.by using them together with a non-literal expression).This means that computations do not overflow and divisions do not truncate in number literal expressions.For example, + - results in the constant 1 (of type ) although intermediate results would not even fit the machine word size.Furthermore, * 8 results in the integer 4 (although non-integers were used in between).If the result is not an integer, an appropriate or type is used whose number of fractional bits is as large as required (approximating the rational number in the worst case).In x = , x will receive the type while in x = it will receive the type because is not finitely representable in binary and will thus be approximated.

Any operator that can be applied to integers can also be applied to number literal expressions as long as the operands are integers.If any of the two is fractional, bit operations are disallowed and exponentiation is disallowed if the exponent is fractional (because that might result in a non-rational number).Note Solidity has a number literal type for each rational number.Integer literals and rational number literals belong to number literal types.Moreover, all number literal expressions (i.e.the expressions that contain only number literals and operators) belong to number literal types.So the number literal expressions 1 + 2 and 2 + 1 both belong to the same number literal type for the rational number three.Note Most finite decimal fractions like are not finitely representable in binary.The correct type for is because that allows to best approximate the number.If you want to use the number together with types like (i.e.), you have to explicitly specify the desired precision: x + .

Warning Division on integer literals used to truncate in earlier versions, but it will now convert into a rational number, i.e.5 / 2 is not equal to 2, but to .Note Number literal expressions are converted into a non-literal type as soon as they are used with non-literal expressions.Even though we know that the value of the expression assigned to b in the following example evaluates to an integer, it still uses fixed point types (and not rational number literals) in between and so the code does not compile a = 1; b = + a + ; String Literals String literals are written with either double or single-quotes ( or ).They do not imply trailing zeroes as in C; represents three bytes not four.As with integer literals, their type can vary, but they are implicitly convertible to , ..., , if they fit, to and to .String literals support escape characters, such as , and .takes a hex value and inserts the appropriate byte, while takes a Unicode codepoint and inserts an UTF-8 sequence.

Hexadecimal Literals Hexademical Literals are prefixed with the keyword and are enclosed in double or single-quotes ().Their content must be a hexadecimal string and their value will be the binary representation of those values.Hexademical Literals behave like String Literals and have the same convertibility restrictions.Enums Enums are one way to create a user-defined type in Solidity.They are explicitly convertible to and from all integer types but implicit conversion is not allowed.The explicit conversions check the value ranges at runtime and a failure causes an exception.Enums needs at least one member.^.0; { { , , , } ; = .; { = .;} () { ;} () { (} } Function Types Function types are the types of functions.Variables of function type can be assigned from functions and function parameters of function type can be used to pass functions to and return functions from function calls.Function types come in two flavours - internal and external functions: Internal functions can only be used inside the current contract (more specifically, inside the current code unit, which also includes internal library functions and inherited functions) because they cannot be executed outside of the context of the current contract.

Calling an internal function is realized by jumping to its entry label, just like when calling a function of the current contract internally.External functions consist of an address and a function signature and they can be passed via and returned from external function calls.Function types are notated as follows: (< >) {|} [] [] [ (< > In contrast to the parameter types, the return types cannot be empty - if the function type should not return anything, the whole part has to be omitted.By default, function types are internal, so the keyword can be omitted.There are two ways to access a function in the current contract: Either directly by its name, f, or using .The former will result in an internal function, the latter in an external function.If a function type variable is not initialized, calling it will result in an exception.The same happens if you call a function after using on it.If external function types are used outside of the context of Solidity, they are treated as the type, which encodes the address followed by the function identifier together in a single type.

Note that public functions of the current contract can be used both as an internal and as an external function.To use f as an internal function, just use f, if you want to use its external form, use .Example that shows how to use internal function types: ^.5; { ( , () () f) ( r){r = .( i = 0; i < .; i) {r[i] = f([i}} ( , ( x, y) () f) ( r){r = [0 ( i = 1; i < .; i) {r = f(r, [i}} ( ) ( r) {r = ( i = 0; i < r.; i) {r[i] = i;}} } { *; ( l) () { .(l((}( x) () { x * x;} ( x, y) () { x + y;} } Another example that uses external function types: ^.; { { ;( ) ;} ; ( ( , ( ) ) {.((,- 1} ( , ) {[(} } { = ( {.(,.} ( ) {(.(} } Note that lambda or inline functions are planned but not yet supported.Reference Types Complex types, i.e.types which do not always fit into 256 bits have to be handled more carefully than the value-types we have already seen.Since copying them can be quite expensive, we have to think about whether we want them to be stored in memory (which is not persisting) or storage (where the state variables are held).

Data location Every complex type, i.e.arrays and structs, has an additional annotation, the “data location”, about whether it is stored in memory or in storage.Depending on the context, there is always a default, but it can be overridden by appending either or to the type.The default for function parameters (including return parameters) is , the default for local variables is and the location is forced to for state variables (obviously).There is also a third data location, “calldata”, which is a non-modifyable non-persistent area where function arguments are stored.Function parameters (not return parameters) of external functions are forced to “calldata” and it behaves mostly like memory.Data locations are important because they change how assignments behave: Assignments between storage and memory and also to a state variable (even from other state variables) always create an independent copy.Assignments to local storage variables only assign a reference though, and this reference always points to the state variable even if the latter is changed in the meantime.

On the other hand, assignments from a memory stored reference type to another memory-stored reference type does not create a copy.^.0; C { x; f( ) {x = ; y = x; y[7 y.= 2; x; g(x h(x } g( ) h( ) } Summary Forced data location: parameters (not return) of external functions: calldata state variables: storage Default data location: parameters (also return) of functions: memory all other local variables: storage Arrays Arrays can have a compile-time fixed size or they can be dynamic.For storage arrays, the element type can be arbitrary (i.e.also other arrays, mappings or structs).For memory arrays, it cannot be a mapping and has to be an ABI type if it is an argument of a publicly-visible function.An array of fixed size k and element type T is written as , an array of dynamic size as .As an example, an array of 5 dynamic arrays of is (note that the notation is reversed when compared to some other languages).

To access the second uint in the third dynamic array, you use (indices are zero-based and access works in the opposite way of the declaration, i.e.shaves off one level in the type from the right).Variables of type and are special arrays.A is similar to , but it is packed tightly in calldata.is equal to but does not allow length or index access (for now).So should always be preferred over because it is cheaper.Note If you want to access the byte-representation of a string s, use / = .Keep in mind that you are accessing the low-level bytes of the UTF-8 representation, and not the individual characters!It is possible to mark arrays and have Solidity create a getter.The numeric index will become a required parameter for the getter.Allocating Memory Arrays Creating arrays with variable length in memory can be done using the keyword.As opposed to storage arrays, it is not possible to resize memory arrays by assigning to the member.^.0; C { f( ) { a = 7 b = (a[6] = 8;} } Array Literals / Inline Arrays Array literals are arrays that are written as an expression and are not assigned to a variable right away.

^.0; C { f {g(1 2, 3} g([3] ) {} } The type of an array literal is a memory array of fixed size whose base type is the common type of the given elements.The type of is , because the type of each of these constants is .Because of that, it was necessary to convert the first element in the example above to .Note that currently, fixed size memory arrays cannot be assigned to dynamically-sized memory arrays, i.e.the following is not possible: ^.0; C { f { x = [(1 3, 4 } It is planned to remove this restriction in the future but currently creates some complications because of how arrays are passed in the ABI.Members length: Arrays have a member to hold their number of elements.Dynamic arrays can be resized in storage (not in memory) by changing the member.This does not happen automatically when attempting to access elements outside the current length.The size of memory arrays is fixed (but dynamic, i.e.it can depend on runtime parameters) once they are created.

push: Dynamic storage arrays and (not ) have a member function called that can be used to append an element at the end of the array.The function returns the new length.Warning It is not yet possible to use arrays of arrays in external functions.Warning Due to limitations of the EVM, it is not possible to return dynamic content from external function calls.The function f in C { { } } will return something if called from web3.js, but not if called from Solidity.The only workaround for now is to use large statically-sized arrays.^.0; {[2] ;[2 ; ([2 ) { = ;} ( , , ) {[0] = ;[1] = ;} ( ) {.= ;} { ; ;.= 0;} ; ( ) { = ;.7;[3] = 8; [2} ([2] ) () { .(}( ) () {[2 = [2 b = ( ( i = 0; i < b.; i)b[i] = (i b;} } Structs Solidity provides a way to define new types in the form of structs, which is shown in the following example: ^.; { { ; ;} { ; ; ; ; ( ) ;} ; ( ) ; ( , ) ( ) { = ; [] = (, , 0, 0} ( ) { c = [c.[c.]= : ., : .c..;} ( ) ( ) { c = [ (c.

;} } The contract does not provide the full functionality of a crowdfunding contract, but it contains the basic concepts necessary to understand structs.Struct types can be used inside mappings and arrays and they can itself contain mappings and arrays.It is not possible for a struct to contain a member of its own type, although the struct itself can be the value type of a mapping member.This restriction is necessary, as the size of the struct has to be finite.Note how in all the functions, a struct type is assigned to a local variable (of the default storage data location).This does not copy the struct but only stores a reference so that assignments to members of the local variable actually write to the state.Of course, you can also directly access the members of the struct without assigning it to a local variable, as in = 0.Mappings Mapping types are declared as .Here can be almost any type except for a mapping, a dynamically sized array, a contract, an enum and a struct.

can actually be any type, including mappings.Mappings can be seen as hash tables which are virtually initialized such that every possible key exists and is mapped to a value whose byte-representation is all zeros: a type’s .The similarity ends here, though: The key data is not actually stored in a mapping, only its hash used to look up the value.Because of this, mappings do not have a length or a concept of a key or value being “set”.Mappings are only allowed for state variables (or as storage reference types in internal functions).It is possible to mark mappings and have Solidity create a getter.The will become a required parameter for the getter and it will return .The can be a mapping too.The getter will have one parameter for each , recursively.^.0; {( ) ; ( ) {[.] = ;} } { f () { (<>(} } Note Mappings are not iterable, but it is possible to implement a data structure on top of them.For an example, see iterable mapping.

Operators Involving LValues If a is an LValue (i.e.a variable or something that can be assigned to), the following operators are available as shorthands: a e is equivalent to a = a + e.The operators , , , , a , and are defined accordingly.and are equivalent to a 1 / a 1 but the expression itself still has the previous value of a.In contrast, and have the same effect on a but return the value after the change.delete a assigns the initial value for the type to a. I.e.for integers it is equivalent to a = 0, but it can also be used on arrays, where it assigns a dynamic array of length zero or a static array of the same length with all elements reset.For structs, it assigns a struct with all members reset.has no effect on whole mappings (as the keys of mappings may be arbitrary and are generally unknown).So if you delete a struct, it will reset all members that are not mappings and also recurse into the members unless they are mappings.However, individual keys and what they map to can be deleted.

It is important to note that a really behaves like an assignment to a, i.e.it stores a new object in a.^.0; { ; ; f { x = ; x; ; y = ; ; } } Conversions between Elementary Types Implicit Conversions If an operator is applied to different types, the compiler tries to implicitly convert one of the operands to the type of the other (the same is true for assignments).In general, an implicit conversion between value-types is possible if it makes sense semantically and no information is lost: is convertible to and to , but is not convertible to (because cannot hold e.g.Furthermore, unsigned integers can be converted to bytes of the same or larger size, but not vice-versa.Any type that can be converted to can also be converted to .Explicit Conversions If the compiler does not allow implicit conversion but you know what you are doing, an explicit type conversion is sometimes possible.Note that this may give you some unexpected behaviour so be sure to test to ensure that the result is what you want!