我构建了一个获取整数参数并返回char数组的函数。
例如,对于13的参数,函数应返回" 0013&#34 ;;对于参数3,函数应该返回" 0003"。
但我没有收到错误,我无法用printf(getInstructionIndex(13));
这是我的代码:
/* get Instruction Index how "0001" or "0010" */
char * getInstructionIndex(int index){
char number1;
char number2;
char number3;
char *str = (char *) malloc(sizeof(char) * 4);
if(index < 10){
number1 = '0';
number2 = '0';
number3 = '0';
str[0] = number1;
str[1] = number2;
str[2] = number3;
str[3] = index;
return str;
}
else{
if(index < 100 && index >= 10){
number1 = '0';
number2 = '0';
str[0] = number1;
str[1] = number2;
str[2] = index;
return str;
}
else
{
if(index < 1000 && index >= 100){
number1 = '0';
str[0] = '0';
str[1] = index;
return str;
}
else
{
str[0] = index;
return str;
}
}
}
free(str);
}
这是我的主要内容:
int main(int argc, char *argv[]){
printf("started\n");
printf(getInstructionIndex(13)); /* i must see 0013*/
printf("stopped\n");
return 0;
}
答案 0 :(得分:3)
<强>问题强>
- 字符串
是不够的str
仅分配了4个字符,对于null终结符- null terminator not added
- 复杂逻辑
- 内存泄漏
- 缺少格式说明符
- cast malloc return
调整后的代码
#include <stdio.h>
#include <stdlib.h>
/* get Instruction Index how "0001" or "0010" */
char * getInstructionIndex(int index){
/* overflow + underflow handling */
if(index < 0 || index > 9999)return 0;
/* allocate enough for the null terminator.. */
char *str = malloc(sizeof(*str) * 5);
/* error handling */
if(!str)
{
return 0;
}
/* simplify logic, use a nice format specifier */
sprintf(str, "%04d", index);
return str;
}
int main(int argc, char *argv[])
{
char *instruction_index;
printf("started\n");
instruction_index = getInstructionIndex(13);
if(!instruction_index)
{
// error handling here..
return 0;
}
/* add format string.. */
printf("%s\n", instruction_index); /* i must see 0013*/
/* release the memory */
free(instruction_index);
printf("stopped\n");
return 0;
}
<强>输出强>
$ gcc -g test.c -o test
$ valgrind ./test
==2713== Memcheck, a memory error detector
==2713== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==2713== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==2713== Command: ./test
==2713==
started
0013
stopped
==2713==
==2713== HEAP SUMMARY:
==2713== in use at exit: 0 bytes in 0 blocks
==2713== total heap usage: 1 allocs, 1 frees, 5 bytes allocated
==2713==
==2713== All heap blocks were freed -- no leaks are possible
==2713==
==2713== For counts of detected and suppressed errors, rerun with: -v
==2713== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
<强>参考强>
答案 1 :(得分:2)
此代码中确实存在内存泄漏,free
应该延迟到打印数组后,例如:
char *str = getInstructionIndex(13)
printf("%s", str); /* i must see 0013*/
free(str);
如果要打印由您应该使用的函数返回的字符串:
printf("%s", str);
还有一件事,你在getInstructionIndex
方法中构造的值需要由字符串终结符\0
终止(或者你将在输出中获得垃圾)。