How to concatenate a std string and an int

Question

I thought this would be really simple but it s presenting some difficulties  If I have  std  string name    John   int age   21    How do I combine them to get a single string  John21

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include  lt sstream gt   template  lt class T gt  inline std  string to string  const T amp  t       std  stringstream ss     ss  lt  lt  t     return ss str        Then your usage would look something like this     std  string szName    John      int numAge   23     szName    to string lt int gt  numAge      cout  lt  lt  szName  lt  lt  endl    Googled  and tested  p

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This is the easiest way   string s   name   std  to string age

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This problem can be done in many ways  I will show it in two ways    Convert the number to string using to string i   Using string streams   Code    include  lt string gt   include  lt sstream gt   include  lt bits stdc   h gt   include  lt iostream gt  using namespace std   int main         string name    John       int age   21       string answer1              Method 1   string s1   to string age        string s1 to string age      Know the integer get converted into string        where as we know that concatenation can easily be done using     in C        answer1   name   s1       cout  lt  lt  answer1  lt  lt  endl          Method 2   Using string streams      ostringstream s2       s2  lt  lt  age       string s3   s2 str       The str   function will convert a number into a string      string answer2           For concatenation of strings       answer2   name   s3       cout  lt  lt  answer2  lt  lt  endl       return 0

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Common Answer  itoa    This is bad   itoa is non-standard  as pointed out here

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include  lt sstream gt   template  lt class T gt  inline std  string to string  const T amp  t       std  stringstream ss     ss  lt  lt  t     return ss str        Then your usage would look something like this     std  string szName    John      int numAge   23     szName    to string lt int gt  numAge      cout  lt  lt  szName  lt  lt  endl    Googled  and tested  p

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include  lt iostream gt   include  lt sstream gt   std  ostringstream o  o  lt  lt  name  lt  lt  age  std  cout  lt  lt  o str

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There are more options possible to use to concatenate integer  or other numerric object  with string  It is Boost Format   include  lt boost format hpp gt   include  lt string gt  int main         using boost  format       int age   22      std  string str age   str format  age is  1      age       and Karma from Boost Spirit  v2    include  lt boost spirit include karma hpp gt   include  lt iterator gt   include  lt string gt  int main         using namespace boost  spirit       int age   22      std  string str age  age is         std  back insert iterator lt std  string gt  sink str age       karma  generate sink  int   age        return 0      Boost Spirit Karma claims to be one of the fastest option for integer to string conversion

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include  lt iostream gt   include  lt string gt   include  lt sstream gt  using namespace std  string itos int i     convert int to string       stringstream s      s  lt  lt  i      return s str        Shamelessly stolen from http   www research att com  bs bs faq2 html

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It seems to me that the simplest answer is to use the sprintf function   sprintf outString   s d  name age

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As a one liner  name    std  to string age

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If you are using MFC  you can use a CString  CString nameAge       nameAge Format   s d    John   21     Managed C   also has a   string formatter

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Here is an implementation of how to append an int to a string using the parsing and formatting facets from the IOStreams library    include  lt iostream gt   include  lt locale gt   include  lt string gt   template  lt class Facet gt  struct erasable facet   Facet       erasable facet     Facet 1           erasable facet           void append int std  string amp  s  int n        erasable facet lt std  num put lt char                                  std  back insert iterator lt std  string gt  gt  gt  facet      std  ios str nullptr        facet put std  back inserter s   str                                       str fill    static cast lt unsigned long gt  n       int main         std  string str    ID         int id   123       append int str  id        std  cout  lt  lt  str     ID  123

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include  lt iostream gt   include  lt string gt   include  lt sstream gt  using namespace std  string itos int i     convert int to string       stringstream s      s  lt  lt  i      return s str        Shamelessly stolen from http   www research att com  bs bs faq2 html

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In C  20 you ll be able to do  auto result   std  format  quot      quot   name  age    In the meantime you can use the  fmt  library  std  format is based on  auto result   fmt  format  quot      quot   name  age    Disclaimer  I m the author of the  fmt  library and C  20 std  format

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If you are using MFC  you can use a CString  CString nameAge       nameAge Format   s d    John   21     Managed C   also has a   string formatter

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include  lt iostream gt   include  lt string gt   include  lt sstream gt  using namespace std  string itos int i     convert int to string       stringstream s      s  lt  lt  i      return s str        Shamelessly stolen from http   www research att com  bs bs faq2 html

User · Answer

This problem can be done in many ways  I will show it in two ways    Convert the number to string using to string i   Using string streams   Code    include  lt string gt   include  lt sstream gt   include  lt bits stdc   h gt   include  lt iostream gt  using namespace std   int main         string name    John       int age   21       string answer1              Method 1   string s1   to string age        string s1 to string age      Know the integer get converted into string        where as we know that concatenation can easily be done using     in C        answer1   name   s1       cout  lt  lt  answer1  lt  lt  endl          Method 2   Using string streams      ostringstream s2       s2  lt  lt  age       string s3   s2 str       The str   function will convert a number into a string      string answer2           For concatenation of strings       answer2   name   s3       cout  lt  lt  answer2  lt  lt  endl       return 0

User · Answer

As a one liner  name    std  to string age

User · Answer

If you have C  11  you can use std  to string   Example   std  string name    John   int age   21   name    std  to string age    std  cout  lt  lt  name    Output   John21

User · Answer

You can concatenate int to string by using the given below simple trick  but note that this only works when integer is of single digit  Otherwise  add integer digit by digit to that string   string name    John   int age   5  char temp   5    0   name   name   temp  cout  lt  lt  name  lt  lt  endl   Output   John5

User · Answer

include  lt sstream gt   template  lt class T gt  inline std  string to string  const T amp  t       std  stringstream ss     ss  lt  lt  t     return ss str        Then your usage would look something like this     std  string szName    John      int numAge   23     szName    to string lt int gt  numAge      cout  lt  lt  szName  lt  lt  endl    Googled  and tested  p

User · Answer

Common Answer  itoa    This is bad   itoa is non-standard  as pointed out here

User · Answer

Common Answer  itoa    This is bad   itoa is non-standard  as pointed out here

User · Answer

In C  20 you ll be able to do  auto result   std  format  quot      quot   name  age    In the meantime you can use the  fmt  library  std  format is based on  auto result   fmt  format  quot      quot   name  age    Disclaimer  I m the author of the  fmt  library and C  20 std  format

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This is the easiest way   string s   name   std  to string age

User · Answer

Common Answer  itoa    This is bad   itoa is non-standard  as pointed out here

User · Answer

include  lt string gt   include  lt sstream gt  using namespace std  string concatenate std  string const amp  name  int i        stringstream s      s  lt  lt  name  lt  lt  i      return s str

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If you d like to use   for concatenation of anything which has an output operator  you can provide a template version of operator    template  lt typename L  typename R gt  std  string operator  L left  R right      std  ostringstream os    os  lt  lt  left  lt  lt  right    return os str        Then you can write your concatenations in a straightforward way   std  string foo  the answer is     int i   42  std  string bar foo   i       std  cout  lt  lt  bar  lt  lt  std  endl    Output   the answer is 42   This isn t the most efficient way  but you don t need the most efficient way unless you re doing a lot of concatenation inside a loop

User · Answer

In C  11  you can use std  to string  e g    auto result   name   std  to string  age

User · Answer

Here is an implementation of how to append an int to a string using the parsing and formatting facets from the IOStreams library    include  lt iostream gt   include  lt locale gt   include  lt string gt   template  lt class Facet gt  struct erasable facet   Facet       erasable facet     Facet 1           erasable facet           void append int std  string amp  s  int n        erasable facet lt std  num put lt char                                  std  back insert iterator lt std  string gt  gt  gt  facet      std  ios str nullptr        facet put std  back inserter s   str                                       str fill    static cast lt unsigned long gt  n       int main         std  string str    ID         int id   123       append int str  id        std  cout  lt  lt  str     ID  123

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As a Qt-related question was closed in favour of this one  here s how to do it using Qt   QString string   QString  Some string  1 with an int somewhere   arg someIntVariable   string append someOtherIntVariable     The string variable now has someIntVariable s value in place of  1 and someOtherIntVariable s value at the end

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It seems to me that the simplest answer is to use the sprintf function   sprintf outString   s d  name age

User · Answer

std  ostringstream     include  lt sstream gt   std  ostringstream s  s  lt  lt   John    lt  lt  age  std  string query s str         std  to string  C  11     std  string query  John     std  to string age        boost  lexical cast     include  lt boost lexical cast hpp gt   std  string query  John     boost  lexical cast lt std  string gt  age

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If you are using MFC  you can use a CString  CString nameAge       nameAge Format   s d    John   21     Managed C   also has a   string formatter

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There is a function I wrote  which takes the int number as the parameter  and convert it to a string literal  This function is dependent on another function that converts a single digit to its char equivalent   char intToChar int num        if  num  lt  10  amp  amp  num  gt   0                return num   48            48 is the number that we add to an integer number to have its character equivalent  see the unsigned ASCII table            else               return               string intToString int num        int digits   0  process  single      string numString      process   num          The following process the number of digits in num     while  process    0                single    process   10      single  now holds the rightmost portion of the int         process    process - single  10             Take out the rightmost number of the int  it s a zero in this portion of the int   then divide it by 10            The above combination eliminates the rightmost portion of the int         digits                process   num          Fill the numString with     times digits     for  int i   0  i  lt  digits  i                  numString                     for  int i   digits-1  i  gt   0  i--                single   process   10          numString i    intToChar   single           process    process - single    10             return numString

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The std  ostringstream is a good method  but sometimes this additional trick might get handy transforming the formatting to a one-liner    include  lt sstream gt   define MAKE STRING tokens                           static cast lt std  ostringstream amp  gt                      std  ostringstream   flush    lt  lt  tokens         str                                                   Now you can format strings like this   int main         int i   123      std  string message   MAKE STRING  i      lt  lt  i       std  cout  lt  lt  message  lt  lt  std  endl     prints   i   123

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In alphabetical order   std  string name    John   int age   21  std  string result      1  with Boost result   name   boost  lexical cast lt std  string gt  age       2  with C  11 result   name   std  to string age       3  with FastFormat Format fastformat  fmt result    0  1    name  age       4  with FastFormat Write fastformat  write result  name  age       5  with the  fmt  library result   fmt  format         name  age       6  with IOStreams std  stringstream sstm  sstm  lt  lt  name  lt  lt  age  result   sstm str        7  with itoa char numstr 21      enough to hold all numbers up to 64-bits result   name   itoa age  numstr  10       8  with sprintf char numstr 21      enough to hold all numbers up to 64-bits sprintf numstr    d   age   result   name   numstr      9  with STLSoft s integer to string char numstr 21      enough to hold all numbers up to 64-bits result   name   stlsoft  integer to string numstr  21  age       10  with STLSoft s winstl  int to string   result   name   winstl  int to string age       11  With Poco NumberFormatter result   name   Poco  NumberFormatter   format age      is safe  but slow  requires Boost  header-only   most all platforms is safe  requires C  11  to string   is already included in  include  lt string gt   is safe  and fast  requires FastFormat  which must be compiled  most all platforms  ditto  is safe  and fast  requires the  fmt  library  which can either be compiled or used in a header-only mode  most all platforms safe  slow  and verbose  requires  include  lt sstream gt   from standard C    is brittle  you must supply a large enough buffer   fast  and verbose  itoa   is a non-standard extension  and not guaranteed to be available for all platforms is brittle  you must supply a large enough buffer   fast  and verbose  requires nothing  is standard C     all platforms is brittle  you must supply a large enough buffer   probably the fastest-possible conversion  verbose  requires STLSoft  header-only   most all platforms safe-ish  you don t use more than one int to string   call in a single statement   fast  requires STLSoft  header-only   Windows-only is safe  but slow  requires Poco C     most all platforms

User · Answer

If you have Boost  you can convert the integer to a string using boost  lexical cast lt std  string gt  age    Another way is to use stringstreams   std  stringstream ss  ss  lt  lt  age  std  cout  lt  lt  name  lt  lt  ss str    lt  lt  std  endl    A third approach would be to use sprintf or snprintf from the C library   char buffer 128   snprintf buffer  sizeof buffer     s d   name c str    age   std  cout  lt  lt  buffer  lt  lt  std  endl    Other posters suggested using itoa  This is NOT a standard function  so your code will not be portable if you use it  There are compilers that don t support it

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include  lt iostream gt   include  lt sstream gt   std  ostringstream o  o  lt  lt  name  lt  lt  age  std  cout  lt  lt  o str

User · Answer

include  lt sstream gt   template  lt class T gt  inline std  string to string  const T amp  t       std  stringstream ss     ss  lt  lt  t     return ss str        Then your usage would look something like this     std  string szName    John      int numAge   23     szName    to string lt int gt  numAge      cout  lt  lt  szName  lt  lt  endl    Googled  and tested  p

User · Answer

As a Qt-related question was closed in favour of this one  here s how to do it using Qt   QString string   QString  Some string  1 with an int somewhere   arg someIntVariable   string append someOtherIntVariable     The string variable now has someIntVariable s value in place of  1 and someOtherIntVariable s value at the end

User · Answer

If you have Boost  you can convert the integer to a string using boost  lexical cast lt std  string gt  age    Another way is to use stringstreams   std  stringstream ss  ss  lt  lt  age  std  cout  lt  lt  name  lt  lt  ss str    lt  lt  std  endl    A third approach would be to use sprintf or snprintf from the C library   char buffer 128   snprintf buffer  sizeof buffer     s d   name c str    age   std  cout  lt  lt  buffer  lt  lt  std  endl    Other posters suggested using itoa  This is NOT a standard function  so your code will not be portable if you use it  There are compilers that don t support it

User · Answer

If you d like to use   for concatenation of anything which has an output operator  you can provide a template version of operator    template  lt typename L  typename R gt  std  string operator  L left  R right      std  ostringstream os    os  lt  lt  left  lt  lt  right    return os str        Then you can write your concatenations in a straightforward way   std  string foo  the answer is     int i   42  std  string bar foo   i       std  cout  lt  lt  bar  lt  lt  std  endl    Output   the answer is 42   This isn t the most efficient way  but you don t need the most efficient way unless you re doing a lot of concatenation inside a loop

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std  ostringstream     include  lt sstream gt   std  ostringstream s  s  lt  lt   John    lt  lt  age  std  string query s str         std  to string  C  11     std  string query  John     std  to string age        boost  lexical cast     include  lt boost lexical cast hpp gt   std  string query  John     boost  lexical cast lt std  string gt  age

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include  lt iostream gt   include  lt string gt   include  lt sstream gt  using namespace std  string itos int i     convert int to string       stringstream s      s  lt  lt  i      return s str        Shamelessly stolen from http   www research att com  bs bs faq2 html

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If you have C  11  you can use std  to string   Example   std  string name    John   int age   21   name    std  to string age    std  cout  lt  lt  name    Output   John21

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There is a function I wrote  which takes the int number as the parameter  and convert it to a string literal  This function is dependent on another function that converts a single digit to its char equivalent   char intToChar int num        if  num  lt  10  amp  amp  num  gt   0                return num   48            48 is the number that we add to an integer number to have its character equivalent  see the unsigned ASCII table            else               return               string intToString int num        int digits   0  process  single      string numString      process   num          The following process the number of digits in num     while  process    0                single    process   10      single  now holds the rightmost portion of the int         process    process - single  10             Take out the rightmost number of the int  it s a zero in this portion of the int   then divide it by 10            The above combination eliminates the rightmost portion of the int         digits                process   num          Fill the numString with     times digits     for  int i   0  i  lt  digits  i                  numString                     for  int i   digits-1  i  gt   0  i--                single   process   10          numString i    intToChar   single           process    process - single    10             return numString

User · Answer

include  lt iostream gt   include  lt sstream gt   std  ostringstream o  o  lt  lt  name  lt  lt  age  std  cout  lt  lt  o str

User · Answer

The std  ostringstream is a good method  but sometimes this additional trick might get handy transforming the formatting to a one-liner    include  lt sstream gt   define MAKE STRING tokens                           static cast lt std  ostringstream amp  gt                      std  ostringstream   flush    lt  lt  tokens         str                                                   Now you can format strings like this   int main         int i   123      std  string message   MAKE STRING  i      lt  lt  i       std  cout  lt  lt  message  lt  lt  std  endl     prints   i   123

User · Answer

If you are using MFC  you can use a CString  CString nameAge       nameAge Format   s d    John   21     Managed C   also has a   string formatter

User · Answer

In C  11  you can use std  to string  e g    auto result   name   std  to string  age

User · Answer

The std  ostringstream is a good method  but sometimes this additional trick might get handy transforming the formatting to a one-liner    include  lt sstream gt   define MAKE STRING tokens                           static cast lt std  ostringstream amp  gt                      std  ostringstream   flush    lt  lt  tokens         str                                                   Now you can format strings like this   int main         int i   123      std  string message   MAKE STRING  i      lt  lt  i       std  cout  lt  lt  message  lt  lt  std  endl     prints   i   123

User · Answer

If you have Boost  you can convert the integer to a string using boost  lexical cast lt std  string gt  age    Another way is to use stringstreams   std  stringstream ss  ss  lt  lt  age  std  cout  lt  lt  name  lt  lt  ss str    lt  lt  std  endl    A third approach would be to use sprintf or snprintf from the C library   char buffer 128   snprintf buffer  sizeof buffer     s d   name c str    age   std  cout  lt  lt  buffer  lt  lt  std  endl    Other posters suggested using itoa  This is NOT a standard function  so your code will not be portable if you use it  There are compilers that don t support it

User · Answer

You can concatenate int to string by using the given below simple trick  but note that this only works when integer is of single digit  Otherwise  add integer digit by digit to that string   string name    John   int age   5  char temp   5    0   name   name   temp  cout  lt  lt  name  lt  lt  endl   Output   John5

User · Answer

include  lt iostream gt   include  lt sstream gt   std  ostringstream o  o  lt  lt  name  lt  lt  age  std  cout  lt  lt  o str

User · Answer

include  lt string gt   include  lt sstream gt  using namespace std  string concatenate std  string const amp  name  int i        stringstream s      s  lt  lt  name  lt  lt  i      return s str

User · Answer

If you have Boost  you can convert the integer to a string using boost  lexical cast lt std  string gt  age    Another way is to use stringstreams   std  stringstream ss  ss  lt  lt  age  std  cout  lt  lt  name  lt  lt  ss str    lt  lt  std  endl    A third approach would be to use sprintf or snprintf from the C library   char buffer 128   snprintf buffer  sizeof buffer     s d   name c str    age   std  cout  lt  lt  buffer  lt  lt  std  endl    Other posters suggested using itoa  This is NOT a standard function  so your code will not be portable if you use it  There are compilers that don t support it

User · Answer

The std  ostringstream is a good method  but sometimes this additional trick might get handy transforming the formatting to a one-liner    include  lt sstream gt   define MAKE STRING tokens                           static cast lt std  ostringstream amp  gt                      std  ostringstream   flush    lt  lt  tokens         str                                                   Now you can format strings like this   int main         int i   123      std  string message   MAKE STRING  i      lt  lt  i       std  cout  lt  lt  message  lt  lt  std  endl     prints   i   123

User · Answer

include  lt string gt   include  lt sstream gt  using namespace std  string concatenate std  string const amp  name  int i        stringstream s      s  lt  lt  name  lt  lt  i      return s str

User · Answer

include  lt string gt   include  lt sstream gt  using namespace std  string concatenate std  string const amp  name  int i        stringstream s      s  lt  lt  name  lt  lt  i      return s str

User · Answer

There are more options possible to use to concatenate integer  or other numerric object  with string  It is Boost Format   include  lt boost format hpp gt   include  lt string gt  int main         using boost  format       int age   22      std  string str age   str format  age is  1      age       and Karma from Boost Spirit  v2    include  lt boost spirit include karma hpp gt   include  lt iterator gt   include  lt string gt  int main         using namespace boost  spirit       int age   22      std  string str age  age is         std  back insert iterator lt std  string gt  sink str age       karma  generate sink  int   age        return 0      Boost Spirit Karma claims to be one of the fastest option for integer to string conversion

User · Answer

It seems to me that the simplest answer is to use the sprintf function   sprintf outString   s d  name age

User · Answer

In alphabetical order   std  string name    John   int age   21  std  string result      1  with Boost result   name   boost  lexical cast lt std  string gt  age       2  with C  11 result   name   std  to string age       3  with FastFormat Format fastformat  fmt result    0  1    name  age       4  with FastFormat Write fastformat  write result  name  age       5  with the  fmt  library result   fmt  format         name  age       6  with IOStreams std  stringstream sstm  sstm  lt  lt  name  lt  lt  age  result   sstm str        7  with itoa char numstr 21      enough to hold all numbers up to 64-bits result   name   itoa age  numstr  10       8  with sprintf char numstr 21      enough to hold all numbers up to 64-bits sprintf numstr    d   age   result   name   numstr      9  with STLSoft s integer to string char numstr 21      enough to hold all numbers up to 64-bits result   name   stlsoft  integer to string numstr  21  age       10  with STLSoft s winstl  int to string   result   name   winstl  int to string age       11  With Poco NumberFormatter result   name   Poco  NumberFormatter   format age      is safe  but slow  requires Boost  header-only   most all platforms is safe  requires C  11  to string   is already included in  include  lt string gt   is safe  and fast  requires FastFormat  which must be compiled  most all platforms  ditto  is safe  and fast  requires the  fmt  library  which can either be compiled or used in a header-only mode  most all platforms safe  slow  and verbose  requires  include  lt sstream gt   from standard C    is brittle  you must supply a large enough buffer   fast  and verbose  itoa   is a non-standard extension  and not guaranteed to be available for all platforms is brittle  you must supply a large enough buffer   fast  and verbose  requires nothing  is standard C     all platforms is brittle  you must supply a large enough buffer   probably the fastest-possible conversion  verbose  requires STLSoft  header-only   most all platforms safe-ish  you don t use more than one int to string   call in a single statement   fast  requires STLSoft  header-only   Windows-only is safe  but slow  requires Poco C     most all platforms

User · Answer

It seems to me that the simplest answer is to use the sprintf function   sprintf outString   s d  name age

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