修改传递给函数的字符数组，C
Modify char array passed to a function, C
我想在一个函数中连接 2 个字符串。但是，我希望函数也修改目标字符串（字符数组）。
到目前为止，我在下面得到了这段代码，但它显示了 'segmentation fault'，我不知道如何解决这个问题。谢谢
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char *my_strcat(char *dest, const char * src) {
char *tab = (char*) malloc(sizeof(char) * (strlen(*dest) + strlen(src) + 1));
if(NULL == tab)
return NULL;
strcpy(tab, dest);
strcpy(tab, src);
free(dest);
dest = (char*)malloc(sizeof(char) * (strlen(tab)+1));
strcpy(dest, tab);
return tab; }
int main(int argc, char **argv) {
char *dst = NULL, *src = NULL, *r = NULL;
int i;
src = malloc(sizeof(char) * 100);
strcpy(src, "fifty");
dst = malloc (sizeof (char *) * 100);
strcpy(src, "four");
r = my_strcat(dst, src);
printf("%s\n", r);
printf("%s\n", dst);
free(r);
free(dst);
free(src);
return 0; }
您的代码中存在几个问题。您可以使用 valgrind, clang-tidy 等工具来帮助您。
这是带有行号的代码
1 /* -*- compile-command: "gcc prog.c; ./a.out"; -*- */
2 #include <stdio.h>
3 #include <stdlib.h>
4 #include <string.h>
5
6 char *my_strcat(char *dest, const char *src)
7 {
8 char *tab = (char *)malloc(sizeof(char) * (strlen(*dest) + strlen(src) + 1));
9 if (NULL == tab)
10 return NULL;
11 strcpy(tab, dest);
12 strcpy(tab, src);
13 free(dest);
14 dest = (char *)malloc(sizeof(char) * (strlen(tab) + 1));
15 strcpy(dest, tab);
16 return tab;
17 }
18
19 int main(int argc, char **argv)
20 {
21 char *dst = NULL, *src = NULL, *r = NULL;
22 int i;
23 src = malloc(sizeof(char) * 100);
24 strcpy(src, "fifty");
25
26 dst = malloc(sizeof(char *) * 100);
27 strcpy(src, "four");
28
29 r = my_strcat(dst, src);
30 printf("%s\n", r);
31 printf("%s\n", dst);
32
33 free(r);
34 free(dst);
35 free(src);
36
37 return 0;
38 }
让我们使用cland-tidy进行静态分析：
clang-tidy-7 prog.c --
打印一堆消息：
8 warnings generated.
/home/picaud/Temp/prog.c:8:46: warning: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage]
char *tab = (char *)malloc(sizeof(char) * (strlen(*dest) + strlen(src) + 1));
^
/home/picaud/Temp/prog.c:26:9: note: Storing uninitialized value
dst = malloc(sizeof(char *) * 100);
^
/home/picaud/Temp/prog.c:29:7: note: Calling 'my_strcat'
r = my_strcat(dst, src);
^
/home/picaud/Temp/prog.c:8:46: note: 1st function call argument is an uninitialized value
char *tab = (char *)malloc(sizeof(char) * (strlen(*dest) + strlen(src) + 1));
^
/home/picaud/Temp/prog.c:8:53: warning: incompatible integer to pointer conversion passing 'char' to parameter of type 'const char *';
etc...
第一行说明dest没有初始化，你可以追溯到：
26 dst = malloc(sizeof(char *) * 100);
27 strcpy(src, "four");
这肯定是一个错误，必须由
替换
26 dst = malloc(sizeof(char *) * 100);
27 strcpy(dst, "four");
现在您可以重新运行 clang-tidy。第一条消息是：
/home/picaud/Temp/prog.c:8:53: warning: incompatible integer to pointer conversion passing 'char' to parameter of type 'const char *';
remove * [clang-diagnostic-int-conversion]
char *tab = (char *)malloc(sizeof(char) * (strlen(*dest) + strlen(src) + 1));
^~~~~
这立即指向另一个错误，替换为：
8 char *tab = (char *)malloc(sizeof(char) * (strlen(*dest) + strlen(src) + 1));
来自
8 char *tab = (char *)malloc(sizeof(char) * (strlen(dest) + strlen(src) + 1));
你还有
/home/picaud/Temp/prog.c:26:9: warning: Result of 'malloc' is converted to a pointer of type 'char', which is incompatible with sizeof operand type 'char *' [clang-analyzer-unix.MallocSizeof]
dst = malloc(sizeof(char *) * 100);
^
因此您必须更换：
dst = malloc(sizeof(char *) * 100);
来自
dst = malloc(sizeof(char) * 100);
re运行ing clang-tidy 仍然显示一些问题：
/home/picaud/Temp/prog.c:27:3: note: Call to function 'strcpy' is insecure as it does not provide bounding of the memory buffer. Replace unbounded copy functions with analogous functions that support length arguments such as 'strlcpy'. CWE-119
/home/picaud/Temp/prog.c:31:3: warning: Use of memory after it is freed [clang-analyzer-unix.Malloc]
printf("%s\n", dst);
^
/home/picaud/Temp/prog.c:26:9: note: Memory is allocated
dst = malloc(sizeof(char) * 100);
^
/home/picaud/Temp/prog.c:29:7: note: Calling 'my_strcat'
r = my_strcat(dst, src);
^
/home/picaud/Temp/prog.c:9:3: note: Taking false branch
if (NULL == tab)
^
/home/picaud/Temp/prog.c:13:3: note: Memory is released
free(dest);
^
/home/picaud/Temp/prog.c:29:7: note: Returning; memory was released via 1st parameter
r = my_strcat(dst, src);
^
/home/picaud/Temp/prog.c:31:3: note: Use of memory after it is freed
printf("%s\n", dst);
我让你检查这一切。在我这边，根据这些警告，我为您的代码获得了这个新版本：
/* -*- compile-command: "gcc prog.c; ./a.out"; -*- */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char *my_strcat(char *dest, const char *src)
{
char *tab = (char *)malloc(sizeof(char) * (strlen(dest) + strlen(src) + 1));
if (NULL == tab)
return NULL;
strcpy(tab, dest);
strcpy(tab+strlen(dest), src);
return tab;
}
int main(int argc, char **argv)
{
char *dst = NULL, *src = NULL, *r = NULL;
int i;
src = malloc(sizeof(char) * 100);
strcpy(src, "fifty");
dst = malloc(sizeof(char) * 100);
strcpy(dst, "four");
r = my_strcat(dst, src);
printf("%s\n", r);
printf("%s\n", dst);
free(r);
free(dst);
free(src);
return 0;
}
当 运行 时，此代码打印：
gcc prog.c; ./a.out
fourfifty
four
您可以使用 valgrind 检查是否存在内存泄漏：
valgrind ./a.out
==4023== Memcheck, a memory error detector
==4023== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==4023== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
==4023== Command: ./a.out
==4023==
fourfifty
four
==4023==
==4023== HEAP SUMMARY:
==4023== in use at exit: 0 bytes in 0 blocks
==4023== total heap usage: 4 allocs, 4 frees, 1,234 bytes allocated
==4023==
==4023== All heap blocks were freed -- no leaks are possible
==4023==
==4023== For counts of detected and suppressed errors, rerun with: -v
==4023== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
好好学习！
dst分配在main中。要在函数中修改该分配，您可以 return 新指针或将指针传递给指针。由于您 return 另一个指针，您必须将指针传递给指针 char **dest 并在函数中进行一些更改以适应该更改。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char *my_strcat ( char **dest, const char * src) {
char *tab = malloc ( sizeof ( char) * (strlen ( *dest) + strlen ( src) + 1));//dereference dest
if ( NULL == tab)
return NULL;
strcpy ( tab, *dest);//dereference dst
strcat ( tab, src);
free ( *dest);//dereference dest
*dest = malloc ( sizeof ( char) * ( strlen ( tab) + 1));//dereference dest
strcpy ( *dest, tab);//dereference dest
return tab;
}
int main(int argc, char **argv) {
char *dst = NULL, *src = NULL, *r = NULL;
src = malloc ( sizeof ( char) * 100);
strcpy ( src, "fifty");
dst = malloc ( sizeof ( char) * 100);
strcpy ( dst, "four");
r = my_strcat ( &dst, src);//use address of dst
printf ( "%s\n", r);
printf ( "%s\n", dst);
free ( r);
free ( dst);
free ( src);
return 0;
}
我想在一个函数中连接 2 个字符串。但是，我希望函数也修改目标字符串（字符数组）。
到目前为止，我在下面得到了这段代码，但它显示了 'segmentation fault'，我不知道如何解决这个问题。谢谢
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char *my_strcat(char *dest, const char * src) {
char *tab = (char*) malloc(sizeof(char) * (strlen(*dest) + strlen(src) + 1));
if(NULL == tab)
return NULL;
strcpy(tab, dest);
strcpy(tab, src);
free(dest);
dest = (char*)malloc(sizeof(char) * (strlen(tab)+1));
strcpy(dest, tab);
return tab; }
int main(int argc, char **argv) {
char *dst = NULL, *src = NULL, *r = NULL;
int i;
src = malloc(sizeof(char) * 100);
strcpy(src, "fifty");
dst = malloc (sizeof (char *) * 100);
strcpy(src, "four");
r = my_strcat(dst, src);
printf("%s\n", r);
printf("%s\n", dst);
free(r);
free(dst);
free(src);
return 0; }
您的代码中存在几个问题。您可以使用 valgrind, clang-tidy 等工具来帮助您。
这是带有行号的代码
1 /* -*- compile-command: "gcc prog.c; ./a.out"; -*- */
2 #include <stdio.h>
3 #include <stdlib.h>
4 #include <string.h>
5
6 char *my_strcat(char *dest, const char *src)
7 {
8 char *tab = (char *)malloc(sizeof(char) * (strlen(*dest) + strlen(src) + 1));
9 if (NULL == tab)
10 return NULL;
11 strcpy(tab, dest);
12 strcpy(tab, src);
13 free(dest);
14 dest = (char *)malloc(sizeof(char) * (strlen(tab) + 1));
15 strcpy(dest, tab);
16 return tab;
17 }
18
19 int main(int argc, char **argv)
20 {
21 char *dst = NULL, *src = NULL, *r = NULL;
22 int i;
23 src = malloc(sizeof(char) * 100);
24 strcpy(src, "fifty");
25
26 dst = malloc(sizeof(char *) * 100);
27 strcpy(src, "four");
28
29 r = my_strcat(dst, src);
30 printf("%s\n", r);
31 printf("%s\n", dst);
32
33 free(r);
34 free(dst);
35 free(src);
36
37 return 0;
38 }
让我们使用cland-tidy进行静态分析：
clang-tidy-7 prog.c --
打印一堆消息：
8 warnings generated. /home/picaud/Temp/prog.c:8:46: warning: 1st function call argument is an uninitialized value [clang-analyzer-core.CallAndMessage] char *tab = (char *)malloc(sizeof(char) * (strlen(*dest) + strlen(src) + 1)); ^ /home/picaud/Temp/prog.c:26:9: note: Storing uninitialized value dst = malloc(sizeof(char *) * 100); ^ /home/picaud/Temp/prog.c:29:7: note: Calling 'my_strcat' r = my_strcat(dst, src); ^ /home/picaud/Temp/prog.c:8:46: note: 1st function call argument is an uninitialized value char *tab = (char *)malloc(sizeof(char) * (strlen(*dest) + strlen(src) + 1)); ^ /home/picaud/Temp/prog.c:8:53: warning: incompatible integer to pointer conversion passing 'char' to parameter of type 'const char *';etc...
第一行说明dest没有初始化，你可以追溯到：
26 dst = malloc(sizeof(char *) * 100);
27 strcpy(src, "four");
这肯定是一个错误，必须由
替换26 dst = malloc(sizeof(char *) * 100);
27 strcpy(dst, "four");
现在您可以重新运行 clang-tidy。第一条消息是：
/home/picaud/Temp/prog.c:8:53: warning: incompatible integer to pointer conversion passing 'char' to parameter of type 'const char *'; remove * [clang-diagnostic-int-conversion] char *tab = (char *)malloc(sizeof(char) * (strlen(*dest) + strlen(src) + 1)); ^~~~~
这立即指向另一个错误，替换为：
8 char *tab = (char *)malloc(sizeof(char) * (strlen(*dest) + strlen(src) + 1));
来自
8 char *tab = (char *)malloc(sizeof(char) * (strlen(dest) + strlen(src) + 1));
你还有
/home/picaud/Temp/prog.c:26:9: warning: Result of 'malloc' is converted to a pointer of type 'char', which is incompatible with sizeof operand type 'char *' [clang-analyzer-unix.MallocSizeof]
dst = malloc(sizeof(char *) * 100);
^
因此您必须更换：
dst = malloc(sizeof(char *) * 100);
来自
dst = malloc(sizeof(char) * 100);
re运行ing clang-tidy 仍然显示一些问题：
/home/picaud/Temp/prog.c:27:3: note: Call to function 'strcpy' is insecure as it does not provide bounding of the memory buffer. Replace unbounded copy functions with analogous functions that support length arguments such as 'strlcpy'. CWE-119
/home/picaud/Temp/prog.c:31:3: warning: Use of memory after it is freed [clang-analyzer-unix.Malloc]
printf("%s\n", dst);
^
/home/picaud/Temp/prog.c:26:9: note: Memory is allocated
dst = malloc(sizeof(char) * 100);
^
/home/picaud/Temp/prog.c:29:7: note: Calling 'my_strcat'
r = my_strcat(dst, src);
^
/home/picaud/Temp/prog.c:9:3: note: Taking false branch
if (NULL == tab)
^
/home/picaud/Temp/prog.c:13:3: note: Memory is released
free(dest);
^
/home/picaud/Temp/prog.c:29:7: note: Returning; memory was released via 1st parameter
r = my_strcat(dst, src);
^
/home/picaud/Temp/prog.c:31:3: note: Use of memory after it is freed
printf("%s\n", dst);
我让你检查这一切。在我这边，根据这些警告，我为您的代码获得了这个新版本：
/* -*- compile-command: "gcc prog.c; ./a.out"; -*- */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char *my_strcat(char *dest, const char *src)
{
char *tab = (char *)malloc(sizeof(char) * (strlen(dest) + strlen(src) + 1));
if (NULL == tab)
return NULL;
strcpy(tab, dest);
strcpy(tab+strlen(dest), src);
return tab;
}
int main(int argc, char **argv)
{
char *dst = NULL, *src = NULL, *r = NULL;
int i;
src = malloc(sizeof(char) * 100);
strcpy(src, "fifty");
dst = malloc(sizeof(char) * 100);
strcpy(dst, "four");
r = my_strcat(dst, src);
printf("%s\n", r);
printf("%s\n", dst);
free(r);
free(dst);
free(src);
return 0;
}
当 运行 时，此代码打印：
gcc prog.c; ./a.out
fourfifty
four
您可以使用 valgrind 检查是否存在内存泄漏：
valgrind ./a.out
==4023== Memcheck, a memory error detector
==4023== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==4023== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
==4023== Command: ./a.out
==4023==
fourfifty
four
==4023==
==4023== HEAP SUMMARY:
==4023== in use at exit: 0 bytes in 0 blocks
==4023== total heap usage: 4 allocs, 4 frees, 1,234 bytes allocated
==4023==
==4023== All heap blocks were freed -- no leaks are possible
==4023==
==4023== For counts of detected and suppressed errors, rerun with: -v
==4023== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
好好学习！
dst分配在main中。要在函数中修改该分配，您可以 return 新指针或将指针传递给指针。由于您 return 另一个指针，您必须将指针传递给指针 char **dest 并在函数中进行一些更改以适应该更改。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char *my_strcat ( char **dest, const char * src) {
char *tab = malloc ( sizeof ( char) * (strlen ( *dest) + strlen ( src) + 1));//dereference dest
if ( NULL == tab)
return NULL;
strcpy ( tab, *dest);//dereference dst
strcat ( tab, src);
free ( *dest);//dereference dest
*dest = malloc ( sizeof ( char) * ( strlen ( tab) + 1));//dereference dest
strcpy ( *dest, tab);//dereference dest
return tab;
}
int main(int argc, char **argv) {
char *dst = NULL, *src = NULL, *r = NULL;
src = malloc ( sizeof ( char) * 100);
strcpy ( src, "fifty");
dst = malloc ( sizeof ( char) * 100);
strcpy ( dst, "four");
r = my_strcat ( &dst, src);//use address of dst
printf ( "%s\n", r);
printf ( "%s\n", dst);
free ( r);
free ( dst);
free ( src);
return 0;
}