Anonymous user
Talk:Function frequency: Difference between revisions
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:: Right. I would propose to change "function" to "identifier" or "token", both in the task's title and in the description (unfortunately, I don't know how to do the former), and leave it open to the individual implementation to be more specific. --[[User:Abu|Abu]] 08:25, 10 December 2011 (UTC)
::: OK, added that, and explained the intent a bit --[[User:Abu|Abu]] 10:50, 11 December 2011 (UTC)
== C example: bugs and oddities ==
Here are some comments about the C example. Some are bugs, others are just strange ways of doing stuff, in case someone wants to fix or improve it. I realize that it's probably better if I actually edit the code instead of just whine about it here, but I really don't feel there's a good solution for this task in C short of writing a full compiler. Whining is so much easier.
<lang c>#define _POSIX_SOURCE
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <stddef.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
struct functionInfo {
char* name;
int timesCalled;
char marked;
};
//strange line continuation; many more to come
//"list" is pointer to pointer, which gets confusing fast
void addToList(struct functionInfo** list, struct functionInfo toAdd, \
size_t* numElements, size_t* allocatedSize) {
//should not hardcode 32; e.g. "inline" is a keyword (this code itself is C99ish)
static const char* keywords[32] = {"auto", "break", "case", "char", "const", \
"continue", "default", "do", "double", \
"else", "enum", "extern", "float", "for", \
"goto", "if", "int", "long", "register", \
"return", "short", "signed", "sizeof", \
"static", "struct", "switch", "typedef", \
"union", "unsigned", "void", "volatile", \
"while"};
/* If the "function" being called is actually a keyword, then ignore it */
for (int i = 0;i < 32;i++) {
if (!strcmp(toAdd.name, keywords[i])) {
return;
}
}
if (!*list) {
*allocatedSize = 10;
*list = calloc(*allocatedSize, sizeof(struct functionInfo));
if (!*list) {
printf("Failed to allocate %d elements of %d bytes each.\n", \
*allocatedSize, sizeof(struct functionInfo));
abort();
}
(*list)[0].name = malloc(strlen(toAdd.name)+1);
if (!(*list)[0].name) {
printf("Failed to allocate %d bytes.\n", strlen(toAdd.name)+1);
abort();
}
strcpy((*list)[0].name, toAdd.name);
(*list)[0].timesCalled = 1;
(*list)[0].marked = 0;
*numElements = 1;
}
else {
char found = 0;
for (unsigned int i = 0;i < *numElements;i++) {
if (!strcmp((*list)[i].name, toAdd.name)) {
found = 1;
(*list)[i].timesCalled++;
break;
}
}
if (!found) {
struct functionInfo* newList = calloc((*allocatedSize)+10, \
sizeof(struct functionInfo));
if (!newList) {
printf("Failed to allocate %d elements of %d bytes each.\n", \
(*allocatedSize)+10, sizeof(struct functionInfo));
abort();
}
memcpy(newList, *list, (*allocatedSize)*sizeof(struct functionInfo));
free(*list);
*allocatedSize += 10;
*list = newList;
(*list)[*numElements].name = malloc(strlen(toAdd.name)+1);
if (!(*list)[*numElements].name) {
printf("Failed to allocate %d bytes.\n", strlen(toAdd.name)+1);
abort();
}
strcpy((*list)[*numElements].name, toAdd.name);
(*list)[*numElements].timesCalled = 1;
(*list)[*numElements].marked = 0;
(*numElements)++;
}
}
}
//absolutely no reason to pass pointer to pointer here
void printList(struct functionInfo** list, size_t numElements) {
char maxSet = 0;
size_t maxIndex = 0;
// a qsort would be much easier to understand
for (unsigned int i = 0;i<10;i++) {
maxSet = 0;
for (size_t j = 0;j<numElements;j++) {
if (!maxSet || (*list)[j].timesCalled > (*list)[maxIndex].timesCalled) {
if (!(*list)[j].marked) {
maxSet = 1;
maxIndex = j;
}
}
}
(*list)[maxIndex].marked = 1;
printf("%s() called %d times.\n", (*list)[maxIndex].name, \
(*list)[maxIndex].timesCalled);
}
}
//same pointer to pointer issue
void freeList(struct functionInfo** list, size_t numElements) {
for (size_t i = 0;i<numElements;i++) {
free((*list)[i].name);
}
free(*list);
}
char* extractFunctionName(char* readHead) {
char* identifier = readHead;
if (isalpha(*identifier) || *identifier == '_') {
while (isalnum(*identifier) || *identifier == '_') {
identifier++;
}
}
/* Search forward for spaces and then an open parenthesis
* but do not include this in the function name.
*/
char* toParen = identifier;
if (toParen == readHead) return NULL;
while (isspace(*toParen)) {//except there could be a backslash line continuation
toParen++;
}
if (*toParen != '(') return NULL;
/* Copy the found function name to the output string */
ptrdiff_t size = (ptrdiff_t)((ptrdiff_t)identifier) \
- ((ptrdiff_t)readHead)+1;
char* const name = malloc(size); //why const? it's going to be written to
if (!name) {
printf("Failed to allocate %d bytes.\n", size);
abort();
}
name[size-1] = '\0';
memcpy(name, readHead, size-1);
/* Function names can't be blank */
if (strcmp(name, "")) {
return name;
}
// this can never happen; if it were to, name would leak
return NULL;
}
int main(int argc, char** argv) {
for (int i = 1;i<argc;i++) {
errno = 0;
FILE* file = fopen(argv[i], "r"); // should use open instead of fopen
// it's unusual, probably just wrong, to check errno before return value
if (errno || !file) {
printf("fopen() failed with error code \"%s\"\n", \
strerror(errno));
abort();
}
char comment = 0;
#define DOUBLEQUOTE 1
#define SINGLEQUOTE 2
int string = 0;
struct functionInfo* functions = NULL;
struct functionInfo toAdd;
size_t numElements = 0;
size_t allocatedSize = 0;
struct stat metaData;
errno = 0;
if (fstat(fileno(file), &metaData) < 0) {
printf("fstat() returned error \"%s\"\n", strerror(errno));
abort();
}
char* mmappedSource = (char*)mmap(NULL, metaData.st_size, PROT_READ, \
MAP_PRIVATE, fileno(file), 0);
if (errno) {
printf("mmap() failed with error \"%s\"\n", strerror(errno));
abort();
}
if (!mmappedSource) {
printf("mmap() returned NULL.\n");
abort();
}
char* readHead = mmappedSource;
while (readHead < mmappedSource + metaData.st_size) {
while (*readHead) { // nonsense check: it's mmap'ed, not null-padded
/* Ignore comments inside strings */
if (!string) {
// if '/' is the last char in source file, strncmp will read into
// undefined memory
if (*readHead == '/' && !strncmp(readHead, "/*", 2)) {
comment = 1;
}
if (*readHead == '*' && !strncmp(readHead, "*/", 2)) {
comment = 0;
}
}
/* Ignore strings inside comments */
if (!comment) {
if (*readHead == '"') {
if (!string) {
string = DOUBLEQUOTE;
}
else if (string == DOUBLEQUOTE) {
/* Only toggle string mode if the quote character
* is not escaped
*/
// if first char of source file is a quote, strncmp will
// read before valid memory position
if (strncmp((readHead-1), "\\\"", 2)) {
string = 0;
}
}
}
if (*readHead == '\'') {
if (!string) {
string = SINGLEQUOTE;
}
else if (string == SINGLEQUOTE) {
// ditto
if (strncmp((readHead-1), "\\\'", 2)) {
string = 0;
}
}
}
}
/* Look for identifiers outside of any comment or string */
if (!comment && !string) {
char* name = extractFunctionName(readHead);
/* Don't read part of an identifier on the next iteration */
if (name) {
toAdd.name = name;
addToList(&functions, toAdd, &numElements, &allocatedSize);
readHead += strlen(name);
}
free(name); //might as well move this into the if block
}
readHead++;
}
}
// ^^ some other situations are not handled; "//" line comment is one,
// common "#if 0" and "if (0)" the other, though the latter requires
// understand syntax instead of just string matching, so probably shouldn't
// be faulted to the code here
errno = 0;
munmap(mmappedSource, metaData.st_size);
if (errno) {
printf("munmap() returned error \"%s\"\n", strerror(errno));
abort();
}
errno = 0;
fclose(file);
if (errno) {
printf("fclose() returned error \"%s\"\n", strerror(errno));
abort();
}
printList(&functions, numElements);
freeList(&functions, numElements);
}
return 0;
}</lang>
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