Message ID | 1255786571-3528-2-git-send-email-aliguori@us.ibm.com |
---|---|
State | New |
Headers | show |
On Sat, 17 Oct 2009 08:36:01 -0500 Anthony Liguori <aliguori@us.ibm.com> wrote: > This allows qstring to be used for dynamic string construction. > > Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> > --- > qstring.c | 37 ++++++++++++++++++++++++++++++++++++- > qstring.h | 4 ++++ > 2 files changed, 40 insertions(+), 1 deletions(-) > > diff --git a/qstring.c b/qstring.c > index 6d411da..441a9e6 100644 > --- a/qstring.c > +++ b/qstring.c > @@ -21,6 +21,16 @@ static const QType qstring_type = { > }; > > /** > + * qstring_new(): Create a new empty QString > + * > + * Return strong reference. > + */ > +QString *qstring_new(void) > +{ > + return qstring_from_str(""); > +} > + > +/** > * qstring_from_str(): Create a new QString from a regular C string > * > * Return strong reference. > @@ -30,12 +40,37 @@ QString *qstring_from_str(const char *str) > QString *qstring; > > qstring = qemu_malloc(sizeof(*qstring)); > - qstring->string = qemu_strdup(str); > + > + qstring->length = strlen(str); > + qstring->capacity = qstring->length; > + > + qstring->string = qemu_malloc(qstring->capacity + 1); > + memcpy(qstring->string, str, qstring->length); > + qstring->string[qstring->length] = 0; Couldn't this be: qstring->string = qemu_strdup(str); qstring->length = qstring->capacity = strlen(str); > + > QOBJECT_INIT(qstring, &qstring_type); > > return qstring; > } > > +/* qstring_append(): Append a C string to a QString > + */ Forgot the 'little roof' in the comment style. :-) > +void qstring_append(QString *qstring, const char *str) > +{ > + size_t len = strlen(str); > + > + if (qstring->capacity < (qstring->length + len)) { > + qstring->capacity += len; > + qstring->capacity *= 2; /* use exponential growth */ > + > + qstring->string = qemu_realloc(qstring->string, qstring->capacity + 1); > + } Why do we need to double it? Wouldn't be enough to only keep track of the current string length and add 'len' to it? We could drop 'capacity' then. > + > + memcpy(qstring->string + qstring->length, str, len); > + qstring->length += len; > + qstring->string[qstring->length] = 0; I would use strcat(). > +} > + > /** > * qobject_to_qstring(): Convert a QObject to a QString > */ > diff --git a/qstring.h b/qstring.h > index e012cb7..65905d4 100644 > --- a/qstring.h > +++ b/qstring.h > @@ -6,10 +6,14 @@ > typedef struct QString { > QObject_HEAD; > char *string; > + size_t length; > + size_t capacity; > } QString; > > +QString *qstring_new(void); > QString *qstring_from_str(const char *str); > const char *qstring_get_str(const QString *qstring); > +void qstring_append(QString *qstring, const char *str); > QString *qobject_to_qstring(const QObject *obj); > > #endif /* QSTRING_H */
Luiz Capitulino wrote: > > qstring = qemu_malloc(sizeof(*qstring)); > > - qstring->string = qemu_strdup(str); > > + > > + qstring->length = strlen(str); > > + qstring->capacity = qstring->length; > > + > > + qstring->string = qemu_malloc(qstring->capacity + 1); > > + memcpy(qstring->string, str, qstring->length); > > + qstring->string[qstring->length] = 0; > > Couldn't this be: > > qstring->string = qemu_strdup(str); > qstring->length = qstring->capacity = strlen(str); Probably to have one call to strlen() instead of two (one inside qemu_strdup()). > > +void qstring_append(QString *qstring, const char *str) > > +{ > > + size_t len = strlen(str); > > + > > + if (qstring->capacity < (qstring->length + len)) { > > + qstring->capacity += len; > > + qstring->capacity *= 2; /* use exponential growth */ > > + > > + qstring->string = qemu_realloc(qstring->string, qstring->capacity + 1); > > + } > > Why do we need to double it? Wouldn't be enough to only keep track > of the current string length and add 'len' to it? We could drop > 'capacity' then. You need exponential growth if large stringes are to be grown in O(n) time where n is the number of characters, appended in small pieces. Think about the time spent copying bytes every time qemu_realloc() is called. If you just add 'len' each time, think about appending 1 byte 10^4 times. It will copy approximately 10^8/2 bytes, which is a lot just to make a string 10^4 bytes long. But += len; *= 2 is not necessary. *= 2 is enough, provided the result is large enough. > > + memcpy(qstring->string + qstring->length, str, len); > > + qstring->length += len; > > + qstring->string[qstring->length] = 0; > > I would use strcat(). Again, that's an extra call to strlen(), traversing the string twice instead of once. Doesn't make much different for small strings, only large ones. -- Jamie
diff --git a/qstring.c b/qstring.c index 6d411da..441a9e6 100644 --- a/qstring.c +++ b/qstring.c @@ -21,6 +21,16 @@ static const QType qstring_type = { }; /** + * qstring_new(): Create a new empty QString + * + * Return strong reference. + */ +QString *qstring_new(void) +{ + return qstring_from_str(""); +} + +/** * qstring_from_str(): Create a new QString from a regular C string * * Return strong reference. @@ -30,12 +40,37 @@ QString *qstring_from_str(const char *str) QString *qstring; qstring = qemu_malloc(sizeof(*qstring)); - qstring->string = qemu_strdup(str); + + qstring->length = strlen(str); + qstring->capacity = qstring->length; + + qstring->string = qemu_malloc(qstring->capacity + 1); + memcpy(qstring->string, str, qstring->length); + qstring->string[qstring->length] = 0; + QOBJECT_INIT(qstring, &qstring_type); return qstring; } +/* qstring_append(): Append a C string to a QString + */ +void qstring_append(QString *qstring, const char *str) +{ + size_t len = strlen(str); + + if (qstring->capacity < (qstring->length + len)) { + qstring->capacity += len; + qstring->capacity *= 2; /* use exponential growth */ + + qstring->string = qemu_realloc(qstring->string, qstring->capacity + 1); + } + + memcpy(qstring->string + qstring->length, str, len); + qstring->length += len; + qstring->string[qstring->length] = 0; +} + /** * qobject_to_qstring(): Convert a QObject to a QString */ diff --git a/qstring.h b/qstring.h index e012cb7..65905d4 100644 --- a/qstring.h +++ b/qstring.h @@ -6,10 +6,14 @@ typedef struct QString { QObject_HEAD; char *string; + size_t length; + size_t capacity; } QString; +QString *qstring_new(void); QString *qstring_from_str(const char *str); const char *qstring_get_str(const QString *qstring); +void qstring_append(QString *qstring, const char *str); QString *qobject_to_qstring(const QObject *obj); #endif /* QSTRING_H */
This allows qstring to be used for dynamic string construction. Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> --- qstring.c | 37 ++++++++++++++++++++++++++++++++++++- qstring.h | 4 ++++ 2 files changed, 40 insertions(+), 1 deletions(-)