08-05-2002
1 .I found the answer .
2 .First , I write another programe .
#include <stdio.h>
#include <string.h>
int main(void)
{
char *p;
p = (char *) malloc(100);
strcpy(p, "asdfasdf");
return 0;
}
It works correctly .
3 . Why ? The point is that :
p is a local varible , when we call do_it(p) , the OS pass a copy of p to child function .Though we malloc memory to p in child function ,the p variable in main function is not changed .
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LEARN ABOUT NETBSD
strndup
STRDUP(3) BSD Library Functions Manual STRDUP(3)
NAME
strdup, strndup -- save a copy of a string
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <string.h>
char *
strdup(const char *str);
char *
strndup(const char *str, size_t len);
DESCRIPTION
The strdup() function allocates sufficient memory for a copy of the string str, does the copy, and returns a pointer to it. The pointer may
subsequently be used as an argument to the function free(3).
If insufficient memory is available, NULL is returned.
The strndup() function copies at most len characters from the string str always NUL terminating the copied string.
EXAMPLES
The following will point p to an allocated area of memory containing the nul-terminated string "foobar":
char *p;
if ((p = strdup("foobar")) == NULL) {
fprintf(stderr, "Out of memory.
");
exit(1);
}
ERRORS
The strdup() function may fail and set the external variable errno for any of the errors specified for the library function malloc(3).
SEE ALSO
free(3), malloc(3), strcpy(3), strlen(3)
STANDARDS
The strdup() function conforms to IEEE Std 1003.1-2001 (``POSIX.1'').
HISTORY
The strdup() function first appeared in 4.4BSD. The strndup() function was added in NetBSD 4.0.
BSD
January 28, 2009 BSD