NAME

       pmExtractValue - extract a performance metric value from a pmResult structure

C SYNOPSIS

       #include <pcp/pmapi.h>

       int pmExtractValue(int valfmt, const pmValue *ival, int itype, pmAtomValue *oval, int otype);

       cc ... -lpcp

DESCRIPTION

       The  pmValue  structure is embedded within the pmResult structure that is used to return one or more per‐
       formance metrics; see pmFetch(3).

       All performance metric values may be encoded in a pmAtomValue union, defined as follows;

            typedef union {
                __int32_t    l;     /* 32-bit signed */
                __uint32_t   ul;    /* 32-bit unsigned */
                __int64_t    ll;    /* 64-bit signed */
                __uint64_t   ull;   /* 64-bit unsigned */
                float        f;     /* 32-bit floating point */
                double       d;     /* 64-bit floating point */
                char         *cp;   /* char ptr */
                pmValueBlock *vbp;  /* pmValueBlock ptr */
            } pmAtomValue;

       The routine pmExtractValue provides a convenient mechanism for extracting values from the pmValue part of
       a pmResult structure, optionally converting the data type, and making the result available to the  appli‐
       cation programmer.

       itype  defines  the  data type of the input value held in ival according to the storage format defined by
       valfmt (see pmFetch(3)).  otype defines the data type of the result to be placed in oval.

       The value for itype is typically extracted from a pmDesc structure, following a call  to  pmLookupDesc(3)
       for a particular performance metric.

       The otype value should be one of the defined PM_TYPE_...  values, that have a 1:1 correspondence with the
       fields in the pmAtomValue union.

       Normally  the  valfmt  parameter would be plucked from the same pmResult structure that provides the ival
       parameter, and if valfmt specifies PM_VAL_INSITU, then the following types are not allowed, as these can‐
       not be encoded in 32-bits; __int64_t, __uint64_t, double, char * and void * (the corresponding itype val‐
       ues are PM_TYPE_64, PM_TYPE_U64, PM_TYPE_DOUBLE, PM_TYPE_STRING, PM_TYPE_AGGREGATE and PM_TYPE_EVENT  re‐
       spectively).  If valfmt specifies PM_VAL_PTR, then the value will be extracted from the associated pmVal‐
       ueBlock  structure,  and the __int32_t, __uint32_t and float options (itype being PM_TYPE_32, PM_TYPE_U32
       and PM_TYPE_FLOAT respectively) are not allowed, as PM_VAL_INSITU is the appropriate encoding for these.

       The following table defines the various possibilities for the type conversion -- the input  type  (itype)
       is shown vertically, and the output type (otype) is shown horizontally.  Y means the conversion is always
       acceptable, N means the conversion can never be performed (the function returns PM_ERR_CONV), P means the
       conversion  may  lose  accuracy  (but  no error status is returned), T means the result may be subject to
       high-order truncation (in which case the function returns PM_ERR_TRUNC) and S means the conversion may be
       impossible due to the sign of the input value (in which case the function returns  PM_ERR_SIGN).   If  an
       error occurs, the value represented by oval will be zero (or NULL).

       Note  that  although some of the conversions involving the types PM_TYPE_STRING and PM_TYPE_AGGREGATE are
       indeed possible, but are marked N - the rationale is that pmExtractValue should not be attempting to  du‐
       plicate functionality already available in the C library via sscanf(3) and sprintf(3).

       No conversion involving the type PM_TYPE_EVENT is supported.

             | 32  |  U32  | 64  |  U64  | FLOAT | DBLE | STRNG | AGGR | EVENT
       ======|=====|=======|=====|=======|=======|======|=======|======|=======
       32    |  Y  |   S   |  Y  |   S   |   P   |  P   |   N   |  N   |   N
       U32   |  T  |   Y   |  Y  |   Y   |   P   |  P   |   N   |  N   |   N
       64    |  T  |  T,S  |  Y  |   S   |   P   |  P   |   N   |  N   |   N
       U64   |  T  |   T   |  T  |   Y   |   P   |  P   |   N   |  N   |   N
       FLOAT | P,T | P,T,S | P,T | P,T,S |   Y   |  Y   |   N   |  N   |   N
       DBLE  | P,T | P,T,S | P,T | P,T,S |   P   |  Y   |   N   |  N   |   N
       STRNG |  N  |   N   |  N  |   N   |   N   |  N   |   Y   |  N   |   N
       AGGR  |  N  |   N   |  N  |   N   |   N   |  N   |   N   |  Y   |   N
       EVENT |  N  |   N   |  N  |   N   |   N   |  N   |   N   |  N   |   N

       In  the cases where multiple conversion errors could occur, the first encountered error will be notified,
       and the order of checking is not defined.

       If the output conversion is to one of the pointer types, i.e. otype is PM_TYPE_STRING  or  PM_TYPE_AGGRE‐
       GATE,  then the value buffer will have been allocated by pmExtractValue(3) using malloc(3), and it is the
       caller's responsibility to free the space when it is no longer required.

       Although this function appears rather complex, it has been constructed to assist the development of  per‐
       formance  tools  that  wish  to  convert  values, whose type is only known via the type field in a pmDesc
       structure, into a canonical type for local processing.  See the pmFetchGroup functions for a simpler  al‐
       ternative.

DIAGNOSTICS

       PM_ERR_CONV

              Impossible conversion, marked by N in above table

       PM_ERR_TRUNC

              High-order truncation occurred

       PM_ERR_SIGN

              Conversion of negative value to unsigned type attempted

SEE ALSO

       PMAPI(3),  pmAtomStr(3),  pmConvScale(3),  pmFetch(3), pmFetchGroup(3), pmLookupDesc(3), pmPrintValue(3),
       pmTypeStr(3), pmUnitsStr(3) and pmUnpackEventRecords(3).

Performance Co-Pilot                                   PCP                                     PMEXTRACTVALUE(3)