How to cast or convert an unsigned int to int in C

Question

My apologies if the question seems weird  I m debugging my code and this seems to be the problem  but I m not sure    Thanks

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If you have a variable unsigned int x   you can convert it to an int using  int x

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IMHO this question is an evergreen  As stated in various answers  the assignment of an unsigned value that is not in the range  0 INT MAX  is implementation defined and might even raise a signal  If the unsigned value is considered to be a two s complement representation of a signed number  the probably most portable way is IMHO the way shown in the following code snippet   include  lt limits h gt  unsigned int u  int i   if  u  lt    unsigned int INT MAX    i    int u     1    else if  u  gt    unsigned int INT MIN    i   - int  u - 1     2    else   i   INT MIN     3      Branch  1  is obvious and cannot invoke overflow or traps  since it is value-preserving   Branch  2  goes through some pains to avoid signed integer overflow by taking the one s complement of the value by bit-wise NOT  casts it to  int   which cannot overflow now   negates the value and subtracts one  which can also not overflow here   Branch  3  provides the poison we have to take on one s complement or sign magnitude targets  because the signed integer representation range is smaller than the two s complement representation range    This is likely to boil down to a simple move on a two s complement target  at least I ve observed such with GCC and CLANG  Also branch  3  is unreachable on such a target -- if one wants to limit the execution to two s complement targets  the code could be condensed to  include  lt limits h gt  unsigned int u  int i   if  u  lt    unsigned int INT MAX    i    int u     1    else   i   - int  u - 1     2     The recipe works with any signed unsigned type pair  and the code is best put into a macro or inline function so the compiler optimizer can sort it out   In which case rewriting the recipe with a ternary operator is helpful  But it s less readable and therefore not a good way to explain the strategy   And yes  some of the casts to  unsigned int  are redundant  but  they might help the casual reader  some compilers issue warnings on signed unsigned compares  because the  implicit cast causes some non-intuitive behavior by language design

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It s as simple as this   unsigned int foo  int bar   10   foo    unsigned int bar    Or vice versa

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Unsigned int can be converted to signed  or vice-versa  by simple expression as shown below      unsigned int z  int y 5  z   unsigned int y       Though not targeted to the question  you would like to read following links     signed to unsigned conversion in C - is it always safe    performance of unsigned vs signed integers   Unsigned and signed values in C    What type-conversions are happening

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It depends on what you want the behaviour to be  An int cannot hold many of the values that an unsigned int can   You can cast as usual   int signedInt    int  myUnsigned    but this will cause problems if the unsigned value is past the max int can hold  This means  half of the possible unsigned values will result in erroneous behaviour unless you specifically watch out for it    You should probably reexamine how you store values in the first place if you re having to convert for no good reason   EDIT  As mentioned by ProdigySim in the comments  the maximum value is platform dependent  But you can access it with INT MAX and UINT MAX   For the usual 4-byte types   4 bytes    4 8  bits   32 bits   If all 32 bits are used  as in unsigned  the maximum value will be 2 32 - 1  or 4 294 967 295   A signed int effectively sacrifices one bit for the sign  so the maximum value will be 2 31 - 1  or 2 147 483 647  Note that this is half of the other value

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Some explain from C  Primer 5th Page 35  If we assign an out-of-range value to an object of unsigned type  the result is the remainder of the value modulo the number of values the target type can hold   For example  an 8-bit unsigned char can hold values from 0 through 255  inclusive  If we assign a value outside the range  the compiler assigns the remainder of that value modulo 256    unsigned char c   -1     assuming 8-bit chars  c has value 255   If we assign an out-of-range value to an object of signed type  the result is undefined  The program might appear to work  it might crash  or it might produce garbage values   Page 160  If any operand is an unsigned type  the type to which the operands are converted depends on the relative sizes of the integral types on the machine       When the signedness differs and the type of the unsigned operand is the same as or larger than that of the signed operand  the signed operand is converted to unsigned   The remaining case is when the signed operand has a larger type than the unsigned operand  In this case  the result is machine dependent  If all values in the unsigned type fit in the large type  then the unsigned operand is converted to the signed type  If the values don t fit  then the signed operand is converted to the unsigned type    For example  if the operands are long and unsigned int  and int and long have the same size  the length will be converted to unsigned int  If the long type has more bits  then the unsigned int will be converted to long   I found reading this book is very helpful

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If an unsigned int and a  signed  int are used in the same expression  the signed int gets implicitly converted to unsigned  This is a rather dangerous feature of the C language  and one you therefore need to be aware of  It may or may not be the cause of your bug  If you want a more detailed answer  you ll have to post some code

[c] How to cast or convert an unsigned int to int in C?

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