I need a mix of strtok and strtok_single

Question

I have the following string that I am trying to parse for variables.

char data[]=\"to=myself@gmail.com&cc=youself@gmail.com&title=&content=how ar         


        

Answer 1

There are two bugs lurking here. One is in strtok_single(). If you run it repeatedly, it does not return the last segment, after the = after signature, unlike strtok().

When that's fixed, there is still a problem with the code in parsePostData(); it returns a pointer to an automatic variable. The copy of the string must be handled differently; the simplest way (which is consistent with using strtok() rather than strtok_r() or strtok_s()) is to make the tCpy variable static.

Test program emt.c

This is a composite program that shows the problems and also a set of fixes. It applies different 'splitter' functions — functions with the same signature as strtok() — to the data. It demonstrates the bug in strtok_single() and that strtok_fixed() fixes that bug. It demonstrates that the code in parsePostData() works correctly when it is fixed and strtok_fixed() is used.

#include 
#include 

/* Function pointer for strtok, strtok_single, strtok_fixed */
typedef char *(*Splitter)(char *str, const char *delims);

/* strtok_single - as quoted in SO 30294129 (from SO 8705844) */
static char *strtok_single(char *str, char const *delims)
{
    static char  *src = NULL;
    char  *p,  *ret = 0;

    if (str != NULL)
        src = str;

    if (src == NULL)
        return NULL;

    if ((p = strpbrk(src, delims)) != NULL)
    {
        *p  = 0;
        ret = src;
        src = ++p;
    }

    return ret;
}

/* strtok_fixed - fixed variation of strtok_single */
static char *strtok_fixed(char *str, char const *delims)
{
    static char  *src = NULL;
    char  *p,  *ret = 0;

    if (str != NULL)
        src = str;

    if (src == NULL || *src == '\0')    // Fix 1
        return NULL;

    ret = src;                          // Fix 2
    if ((p = strpbrk(src, delims)) != NULL)
    {
        *p  = 0;
        //ret = src;                    // Unnecessary
        src = ++p;
    }
    else
        src += strlen(src);

    return ret;
}

/* Raw test of splitter functions */
static void parsePostData1(const char *s, const char *t, Splitter splitter)
{
    static char tCpy[512];
    strcpy(tCpy, t);
    char *pch = splitter(tCpy, "=&");
    while (pch != NULL)
    {
        printf("  [%s]\n", pch);
        if (strcmp(pch, s) == 0)
            printf("matches %s\n", s);
        pch = splitter(NULL, "=&");
    }
}

/* Fixed version of parsePostData() from SO 30294129 */
static char *parsePostData2(const char *s, const char *t, Splitter splitter)
{
    static char tCpy[512];
    strcpy(tCpy, t);
    char *pch = splitter(tCpy, "=&");
    while (pch != NULL)
    {
        if (strcmp(pch, s) == 0)
        {
            pch = splitter(NULL, "&");
            return pch;
        }
        else
        {
            pch = splitter(NULL, "=&");
        }
    }
    return NULL;
}

/* Composite test program */
int main(void)
{
    char data[] = "to=myself@gmail.com&cc=youself@gmail.com&title=&content=how are you?&signature=best regards.";
    char *tags[] = { "to", "cc", "title", "content", "signature" };
    enum { NUM_TAGS = sizeof(tags) / sizeof(tags[0]) };

    printf("\nCompare variants on strtok()\n");
    {
        int i = NUM_TAGS - 1;
        printf("strtok():\n");
        parsePostData1(tags[i], data, strtok);
        printf("strtok_single():\n");
        parsePostData1(tags[i], data, strtok_single);
        printf("strtok_fixed():\n");
        parsePostData1(tags[i], data, strtok_fixed);
    }

    printf("\nCompare variants on strtok()\n");
    for (int i = 0; i < NUM_TAGS; i++)
    {
        char *value1 = parsePostData2(tags[i], data, strtok);
        printf("strtok: [%s] = [%s]\n", tags[i], value1);
        char *value2 = parsePostData2(tags[i], data, strtok_single);
        printf("single: [%s] = [%s]\n", tags[i], value2);
        char *value3 = parsePostData2(tags[i], data, strtok_fixed);
        printf("fixed:  [%s] = [%s]\n", tags[i], value3);
    }

    return 0;
}

Example output from emt

Compare variants on strtok()
strtok():
  [to]
  [myself@gmail.com]
  [cc]
  [youself@gmail.com]
  [title]
  [content]
  [how are you?]
  [signature]
matches signature
  [best regards.]
strtok_single():
  [to]
  [myself@gmail.com]
  [cc]
  [youself@gmail.com]
  [title]
  []
  [content]
  [how are you?]
  [signature]
matches signature
strtok_fixed():
  [to]
  [myself@gmail.com]
  [cc]
  [youself@gmail.com]
  [title]
  []
  [content]
  [how are you?]
  [signature]
matches signature
  [best regards.]

And:

Compare variants on strtok()
✓ strtok: [to] = [myself@gmail.com]
✓ single: [to] = [myself@gmail.com]
✓ fixed:  [to] = [myself@gmail.com]
✓ strtok: [cc] = [youself@gmail.com]
✓ single: [cc] = [youself@gmail.com]
✓ fixed:  [cc] = [youself@gmail.com]
✕ strtok: [title] = [content=how are you?]
✓ single: [title] = []
✓ fixed:  [title] = []
✓ strtok: [content] = [how are you?]
✓ single: [content] = [how are you?]
✓ fixed:  [content] = [how are you?]
✓ strtok: [signature] = [best regards.]
✕ single: [signature] = [(null)]
✓ fixed:  [signature] = [best regards.]

The correct (✓ = U+2713) and incorrect (✕ = U+2715) marks were added manually when posting the answer.

Observe how only the lines tagged 'fixed' contain exactly what is wanted each time around.