Convert hex string char to int

Question

I have a char   that contains a value such as  0x1800785  but the function I want to give the value to requires an int  how can I convert this to an int  I have searched around but cannot find an answer  Thanks

User · Answer

Try below block of code  its working for me   char  p    0x820   uint16 t intVal  sscanf p    x    amp intVal    printf  value x   x -  d   intVal  intVal     Output is   value x  820 - 2080

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i have done a similar thing  think it might help u its actually working for me  int main    int co 8  i char ch 8  printf  please enter the string    scanf   s  ch  for i 0 i lt  7 i    if  ch i  gt   A   amp  amp  ch i  lt   F    co i   unsigned int ch i - A  10  else if  ch i  gt   0   amp  amp  ch i  lt   9    co i   unsigned int ch i - 0  0      here i have only taken a string of 8 characters  if u want u can add similar logic for  a  to  f  to give their equivalent hex values i haven t done that cause i didn t needed it

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Something like this could be useful   char str      0x1800785   int num   sscanf str    x    amp num   printf  0x x  i n   num  num      Read man sscanf

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One quick  amp  dirty solution       makes a number from two ascii hexa characters int ahex2int char a  char b        a    a  lt    9     a -  0     a  amp  0x7    9      b    b  lt    9     b -  0     b  amp  0x7    9       return  a  lt  lt  4    b      You have to be sure your input is correct  no validation included  one could say it is C   Good thing it is quite compact  it works with both  A  to  F  and  a  to  f    The approach relies on the position of alphabet characters in the ASCII table  let s peek e g  to Wikipedia  https   en wikipedia org wiki ASCII  media File USASCII code chart png   Long story short  the numbers are below the characters  so the numeric characters  0 to 9  are easily converted by subtracting the code for zero  The alphabetic characters  A to F  are read by zeroing other than last three bits  effectively making it work with either upper- or lowercase   subtracting one  because after the bit masking  the alphabet starts on position one  and adding ten  because A to F represent 10th to 15th value in hexadecimal code   Finally  we need to combine the two digits that form the lower and upper nibble of the encoded number   Here we go with same approach  with minor variations     include  lt stdio h gt      takes a null-terminated string of hexa characters and tries to     convert it to numbers long ahex2num unsigned char  in        unsigned char  pin   in     lets use pointer to loop through the string     long out   0      here we accumulate the result      while  pin    0           out  lt  lt   4     we have one more input character  so                        we shift the accumulated interim-result one order up         out       pin  lt   A      pin  amp  0xF     pin  amp  0x7    9     add the new nibble         pin       go ahead            return out        main function will test our conversion fn int main void         unsigned char str      1800785       no 0x prefix  please     long num       num   ahex2num str       call the function      printf  Input   s n  str       print input string     printf  Output   x n  num       print the converted number back as hexa     printf  Check   ld    ld  n  num 0x1800785       check the numeric values matches      return 0

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This is a function to directly convert hexadecimal containing char array to an integer which needs no extra library  int hexadecimal2int char  hdec        int finalval   0      while   hdec                     int onebyte    hdec                      if  onebyte  gt    0   amp  amp  onebyte  lt    9   onebyte   onebyte -  0            else if  onebyte  gt    a   amp  amp  onebyte  lt   f    onebyte   onebyte -  a    10           else if  onebyte  gt    A   amp  amp  onebyte  lt   F    onebyte   onebyte -  A    10                      finalval    finalval  lt  lt  4     onebyte  amp  0xF             finalval   finalval - 524288      return finalval

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Or if you want to have your own implementation  I wrote this quick function as an example          hex2int    take a hex string and convert it to a 32bit number  max 8 hex digits      uint32 t hex2int char  hex        uint32 t val   0      while   hex               get current character then increment         uint8 t byte    hex                transform hex character to the 4bit equivalent number  using the ascii table indexes         if  byte  gt    0   amp  amp  byte  lt    9   byte   byte -  0           else if  byte  gt    a   amp  amp  byte  lt   f   byte   byte -  a    10          else if  byte  gt    A   amp  amp  byte  lt   F   byte   byte -  A    10                 shift 4 to make space for new digit  and add the 4 bits of the new digit          val    val  lt  lt  4     byte  amp  0xF             return val

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I made a librairy to make Hexadecimal   Decimal conversion without the use of stdio h  Very simple to use    unsigned hexdec  const char  hex  const int s hex     Before the first conversion intialize the array used for conversion with    void init hexdec       Here the link on github   https   github com kevmuret libhex

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So  after a while of searching  and finding out that strtol is quite slow  I ve coded my own function  It only works for uppercase on letters  but adding lowercase functionality ain t a problem   int hexToInt PCHAR  hex  int offset   0  int size   6        int  result   0      DWORD  resultPtr   reinterpret cast lt DWORD gt   amp  result       for int i 0 i lt size i  2                int  multiplierFirstValue   0   addonSecondValue   0           char  firstChar    hex offset   i           if  firstChar  gt   0x30  amp  amp   firstChar  lt   0x39               multiplierFirstValue    firstChar - 0x30          else if  firstChar  gt   0x41  amp  amp   firstChar  lt   0x46               multiplierFirstValue   10     firstChar - 0x41            char  secndChar    hex offset   i   1           if  secndChar  gt   0x30  amp  amp   secndChar  lt   0x39               addonSecondValue    secndChar - 0x30          else if  secndChar  gt   0x41  amp  amp   secndChar  lt   0x46               addonSecondValue   10     secndChar - 0x41              BYTE     resultPtr    size   2  -  i   2  - 1     BYTE   multiplierFirstValue   16    addonSecondValue             return  result      Usage   char  someHex     CCFF00FF   int hexDevalue   hexToInt someHex  1  8     1 because the hex we want to convert starts at offset 1  and 8 because it s the hex length   Speedtest  1 000 000 calls    strtol   0 4400s hexToInt   0 1100s

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I know this is really old but I think the solutions looked too complicated   Try this in VB   Public Function HexToInt sHEX as String  as long Dim iLen as Integer Dim i as Integer  Dim SumValue as Long  Dim iVal as long Dim AscVal as long      iLen   Len sHEX      For i   1 to Len sHEX        AscVal   Asc UCase Mid  sHEX  i   1          If AscVal  gt   48 And AscVal   lt   57 Then         iVal    AscVal - 48       ElseIf AscVal  gt   65 And AscVal  lt   70 Then         iVal   AscVal - 55       End If        SumValue   SumValue   iVal   16    iLen- i      Next i      HexToInt    SumValue End Function

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Assuming you mean it s a string  how about strtol

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Have you tried strtol     strtol - convert string to a long integer   Example   const char  hexstring    abcdef0   int number    int strtol hexstring  NULL  16     In case the string representation of the number begins with a 0x prefix  one must should use 0 as base   const char  hexstring    0xabcdef0   int number    int strtol hexstring  NULL  0      It s as well possible to specify an explicit base such as 16  but I wouldn t recommend introducing redundancy

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Use strtol if you have libc available like the top answer suggests  However if you like custom stuff or are on a microcontroller without libc or so  you may want a slightly optimized version without complex branching    include  lt inttypes h gt           xtou64    Take a hex string and convert it to a 64bit number  max 16 hex digits      The string must only contain digits and valid hex characters      uint64 t xtou64 const char  str        uint64 t res   0      char c       while   c    str               char v    c  amp  0xF     c  gt  gt  6      c  gt  gt  3   amp  0x8           res    res  lt  lt  4     uint64 t  v             return res       The bit shifting magic boils down to  Just use the last 4 bits  but if it is an non digit  then also add 9

[c] Convert hex string (char []) to int?

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