Binary strstr

strstr is a Standard C function but it cannot handle '\0'. Here is the modified version to handle binary data. The bstrstr confronts to strstr and returns char*

bstrstr Select all


char *(bstrstr)(const char *s1, size_t l1, const char *s2, size_t l2) {
/* find first occurrence of s2[] in s1[] for length l1*/
const char *ss1 = s1;
const char *ss2 = s2;
/* handle special case */
if (l1 == 0)
return (NULL);
if (l2 == 0)
return ((char *)s1);

/* match prefix */
for (; (s1 = bstrchr(s1, *s2, ss1-s1+l1)) != NULL && ss1-s1+l1!=0; ++s1) {

/* match rest of prefix */
const char *sc1, *sc2;
for (sc1 = s1, sc2 = s2; ;)
if (++sc2 >= ss2+l2)
return ((char *)s1);
else if (*++sc1 != *sc2)
break;
}
return (NULL);
}


It needs a bstrchr function as well.

bstrchr Select all


char *(bstrchr) (const char *s, int c, size_t l) {
/* find first occurrence of c in char s[] for length l*/
const char ch = c;
/* handle special case */
if (l == 0)
return (NULL);

for (; *s != ch; ++s, --l)
if (l == 0)
return (NULL);
return ((char*)s);
}


here is the testing program

bstsrstr_test.c Select all


/* bstsrstr test */
#include <stdio.h>
#include <string.h>
#include <ctype.h>

char *(bstrchr) (const char *s, int c, size_t l) {
/* find first occurrence of c in char s[] for length l*/
const char ch = c;
/* handle special case */
if (l == 0)
return (NULL);

for (; *s != ch; ++s, --l)
if (l == 0)
return (NULL);
return ((char*)s);
}

char *(bstrstr)(const char *s1, size_t l1, const char *s2, size_t l2) {
/* find first occurrence of s2[] in s1[] for length l1*/
const char *ss1 = s1;
const char *ss2 = s2;
/* handle special case */
if (l1 == 0)
return (NULL);
if (l2 == 0)
return ((char *)s1);

/* match prefix */
for (; (s1 = bstrchr(s1, *s2, ss1-s1+l1)) != NULL && ss1-s1+l1!=0; ++s1) {

/* match rest of prefix */
const char *sc1, *sc2;
for (sc1 = s1, sc2 = s2; ;)
if (++sc2 >= ss2+l2)
return ((char *)s1);
else if (*++sc1 != *sc2)
break;
}
return (NULL);
}

void printbstr(const char *s, size_t l) {
for (; l!=0 ; --l) {
printf("%c", isprint(*(s))?*(s):'.');
s++;
}
printf("\n");
}

void test(const char *s1, size_t l1, const char *s2, size_t l2) {
printf("\n");
printbstr(s1, l1);
printf("locate ");
printbstr(s2, l2);
const char *r = bstrstr(s1,l1,s2,l2);
if (!r)
printf("not found\n");
else {
printf("result ");
printbstr(r, l1-(size_t)(r-s1));
}
}

int main () {
char *s1 = "I\0am a\0manz";
size_t l1 = 11;

printf("bstrstr test\n------\n");
printbstr(s1, l1);
printf("locate \\%c:%s\n", '0', bstrchr(s1,'\0',l1));
printf("locate %c:%s\n", 'I', bstrchr(s1,'I',l1));
printf("locate %c:%s\n", 'a', bstrchr(s1,'a',l1));
printf("locate %c:%s\n", 'n', bstrchr(s1,'n',l1));
printf("locate %c:%s\n", 'i', bstrchr(s1,'i',l1));
printf("locate %c:%s\n", 'z', bstrchr(s1,'z',l1));

test(s1, l1, "a\0m", 3);
test(s1, l1, "z", 1);
test(s1, l1, "I", 1);
test(s1, l1, "am a", 4);
test(s1, l1, "anz", 3);
test(s1, l1, "ax", 2);
test(s1, l1, "\0x", 2);
test(s1, l1, " x", 2);
test(s1, l1, "\0a", 2);
test(s1, l1, "a\0m", 3);
test(s1, l1, "x", 1);
test(s1, l1, "z", 1);

return 0;
}