What s the difference between size t and int in C

Question

In several C   examples I see a use of the type size t where I would have used a simple int  What s the difference  and why size t should be better

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size t is the type used to represent sizes  as its names implies   Its platform  and even potentially implementation  dependent  and should be used only for this purpose  Obviously  representing a size  size t is unsigned  Many stdlib functions  including malloc  sizeof and various string operation functions use size t as a datatype   An int is signed by default  and even though its size is also platform dependant  it will be a fixed 32bits on most modern machine  and though size t is 64 bits on 64-bits architecture  int remain 32bits long on those architectures    To summarize   use size t to represent the size of an object and int  or long  in other cases

User · Answer

From the friendly Wikipedia   The stdlib h and stddef h header files define a datatype called size t which is used to represent the size of an object  Library functions that take sizes expect them to be of type size t  and the sizeof operator evaluates to size t  The actual type of size t is platform-dependent  a common mistake is to assume size t is the same as unsigned int  which can lead to programming errors  particularly as 64-bit architectures become more prevalent   Also  check Why size t matters

User · Answer

From the friendly Wikipedia   The stdlib h and stddef h header files define a datatype called size t which is used to represent the size of an object  Library functions that take sizes expect them to be of type size t  and the sizeof operator evaluates to size t  The actual type of size t is platform-dependent  a common mistake is to assume size t is the same as unsigned int  which can lead to programming errors  particularly as 64-bit architectures become more prevalent   Also  check Why size t matters

User · Answer

size t is the type used to represent sizes  as its names implies   Its platform  and even potentially implementation  dependent  and should be used only for this purpose  Obviously  representing a size  size t is unsigned  Many stdlib functions  including malloc  sizeof and various string operation functions use size t as a datatype   An int is signed by default  and even though its size is also platform dependant  it will be a fixed 32bits on most modern machine  and though size t is 64 bits on 64-bits architecture  int remain 32bits long on those architectures    To summarize   use size t to represent the size of an object and int  or long  in other cases

User · Answer

It s because size t can be anything other than an int  maybe a struct   The idea is that it decouples it s job from the underlying type

User · Answer

The size t type is defined as the unsigned integral type of the sizeof operator   In the real world  you will often see int defined as 32 bits  for backward compatibility  but size t defined as 64 bits  so you can declare arrays and structures more than 4 GiB in size  on 64-bit platforms   If a long int is also 64-bits  this is called the LP64 convention  if long int is 32 bits but long long int and pointers are 64 bits  that   s LLP64  You also might get the reverse  a program that uses 64-bit instructions for speed  but 32-bit pointers to save memory   Also  int is signed and size t is unsigned   There were historically a number of other platforms where addresses were wider or shorter than the native size of int   In fact  in the    70s and early     80s  this was more common than not  all the popular 8-bit microcomputers had 8-bit registers and 16-bit addresses  and the transition between 16 and 32 bits also produced many machines that had addresses wider than their registers   I occasionally still see questions here about Borland Turbo C for MS-DOS  whose Huge memory mode had 20-bit addresses stored in 32 bits on a 16-bit CPU  but which could support the 32-bit instruction set of the 80386   the Motorola 68000 had a 16-bit ALU with 32-bit registers and addresses  there were IBM mainframes with 15-bit  24-bit or 31-bit addresses   You also still see different ALU and address-bus sizes in embedded systems   Any time int is smaller than size t  and you try to store the size or offset of a very large file or object in an unsigned int  there is the possibility that it could overflow and cause a bug   With an int  there is also the possibility of getting a negative number  If an int or unsigned int is wider  the program will run correctly but waste memory   You should generally use the correct type for the purpose if you want portability   A lot of people will recommend that you use signed math instead of unsigned  to avoid nasty  subtle bugs like 1U  lt  -3    For that purpose  the standard library defines ptrdiff t in  lt stddef h gt  as the signed type of the result of subtracting a pointer from another   That said  a workaround might be to bounds-check all addresses and offsets against INT MAX and either 0 or INT MIN as appropriate  and turn on the compiler warnings about comparing signed and unsigned quantities in case you miss any   You should always  always  always be checking your array accesses for overflow in C anyway

User · Answer

The definition of SIZE T is found at  https   msdn microsoft com en-us library cc441980 aspx and https   msdn microsoft com en-us library cc230394 aspx  Pasting here the required information   SIZE T is a ULONG PTR representing the maximum number of bytes to which a pointer can point   This type is declared as follows   typedef ULONG PTR SIZE T    A ULONG PTR is an unsigned long type used for pointer precision  It is used when casting a pointer to a long type to perform pointer arithmetic   This type is declared as follows   typedef unsigned   int3264 ULONG PTR

User · Answer

size t is the type used to represent sizes  as its names implies   Its platform  and even potentially implementation  dependent  and should be used only for this purpose  Obviously  representing a size  size t is unsigned  Many stdlib functions  including malloc  sizeof and various string operation functions use size t as a datatype   An int is signed by default  and even though its size is also platform dependant  it will be a fixed 32bits on most modern machine  and though size t is 64 bits on 64-bits architecture  int remain 32bits long on those architectures    To summarize   use size t to represent the size of an object and int  or long  in other cases

User · Answer

The size t type is defined as the unsigned integral type of the sizeof operator   In the real world  you will often see int defined as 32 bits  for backward compatibility  but size t defined as 64 bits  so you can declare arrays and structures more than 4 GiB in size  on 64-bit platforms   If a long int is also 64-bits  this is called the LP64 convention  if long int is 32 bits but long long int and pointers are 64 bits  that   s LLP64  You also might get the reverse  a program that uses 64-bit instructions for speed  but 32-bit pointers to save memory   Also  int is signed and size t is unsigned   There were historically a number of other platforms where addresses were wider or shorter than the native size of int   In fact  in the    70s and early     80s  this was more common than not  all the popular 8-bit microcomputers had 8-bit registers and 16-bit addresses  and the transition between 16 and 32 bits also produced many machines that had addresses wider than their registers   I occasionally still see questions here about Borland Turbo C for MS-DOS  whose Huge memory mode had 20-bit addresses stored in 32 bits on a 16-bit CPU  but which could support the 32-bit instruction set of the 80386   the Motorola 68000 had a 16-bit ALU with 32-bit registers and addresses  there were IBM mainframes with 15-bit  24-bit or 31-bit addresses   You also still see different ALU and address-bus sizes in embedded systems   Any time int is smaller than size t  and you try to store the size or offset of a very large file or object in an unsigned int  there is the possibility that it could overflow and cause a bug   With an int  there is also the possibility of getting a negative number  If an int or unsigned int is wider  the program will run correctly but waste memory   You should generally use the correct type for the purpose if you want portability   A lot of people will recommend that you use signed math instead of unsigned  to avoid nasty  subtle bugs like 1U  lt  -3    For that purpose  the standard library defines ptrdiff t in  lt stddef h gt  as the signed type of the result of subtracting a pointer from another   That said  a workaround might be to bounds-check all addresses and offsets against INT MAX and either 0 or INT MIN as appropriate  and turn on the compiler warnings about comparing signed and unsigned quantities in case you miss any   You should always  always  always be checking your array accesses for overflow in C anyway

User · Answer

It s because size t can be anything other than an int  maybe a struct   The idea is that it decouples it s job from the underlying type

User · Answer

It s because size t can be anything other than an int  maybe a struct   The idea is that it decouples it s job from the underlying type

User · Answer

size t is the type used to represent sizes  as its names implies   Its platform  and even potentially implementation  dependent  and should be used only for this purpose  Obviously  representing a size  size t is unsigned  Many stdlib functions  including malloc  sizeof and various string operation functions use size t as a datatype   An int is signed by default  and even though its size is also platform dependant  it will be a fixed 32bits on most modern machine  and though size t is 64 bits on 64-bits architecture  int remain 32bits long on those architectures    To summarize   use size t to represent the size of an object and int  or long  in other cases

User · Answer

It s because size t can be anything other than an int  maybe a struct   The idea is that it decouples it s job from the underlying type

User · Answer

From the friendly Wikipedia   The stdlib h and stddef h header files define a datatype called size t which is used to represent the size of an object  Library functions that take sizes expect them to be of type size t  and the sizeof operator evaluates to size t  The actual type of size t is platform-dependent  a common mistake is to assume size t is the same as unsigned int  which can lead to programming errors  particularly as 64-bit architectures become more prevalent   Also  check Why size t matters

User · Answer

From the friendly Wikipedia   The stdlib h and stddef h header files define a datatype called size t which is used to represent the size of an object  Library functions that take sizes expect them to be of type size t  and the sizeof operator evaluates to size t  The actual type of size t is platform-dependent  a common mistake is to assume size t is the same as unsigned int  which can lead to programming errors  particularly as 64-bit architectures become more prevalent   Also  check Why size t matters

User · Answer

The definition of SIZE T is found at  https   msdn microsoft com en-us library cc441980 aspx and https   msdn microsoft com en-us library cc230394 aspx  Pasting here the required information   SIZE T is a ULONG PTR representing the maximum number of bytes to which a pointer can point   This type is declared as follows   typedef ULONG PTR SIZE T    A ULONG PTR is an unsigned long type used for pointer precision  It is used when casting a pointer to a long type to perform pointer arithmetic   This type is declared as follows   typedef unsigned   int3264 ULONG PTR

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