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C语言: Newb translating code from javascript to C,代码包含malloc、strncpy、指针

转载 作者:行者123 更新时间:2023-11-30 15:56:12 24 4
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我正在转换(从 javascript)一个程序,该程序将采用可变长度的字符串(但始终低于 100 个字符)并返回单个变量中字符串中包含的数据。这是我的代码的第一部分,显然,我对 C 和一般编程很陌生。该代码适用于代码的第一部分,但是学习如何正确编码这将使我知道如何编码其余部分。

我需要:

  • 前 4 位数字存储为“stringID”
  • 要存储为“myindicator”的第 5 位数字
  • 第 6 到(指示器 + 6)位数字将存储为“var1”

输入示例:

'12345678901234567890123'

示例输出:

  • 字符串 ID = 1234
  • 我的指标 = 5
  • var1 = 67890123456

当我运行该程序时,它返回“String ID: H>a”,然后程序崩溃。任何帮助,将不胜感激。不,这不是家庭作业。

int main()

{
char mystring[100];
char *stringID;
int nep;
int *myindicator;
char *var1;


nep = 0;
printf("Please enter your CODE\n");
scanf("%s", &mystring);

stringID = (char *)malloc(4 * sizeof(char));

if(NULL != stringID)
{

strncpy(stringID, mystring, 4);
stringID[4] = '\0';
free(stringID);
nep = nep +4;
printf("stringID: %s\n",myindicator);
}


if(NULL != myindicator)
{
strncpy(myindicator, (mystring+nep, 1);
nep++;
myindicator = *myindicator - '0';
printf("Indicator : %d\n",myindicator);
}

var1 = (char *)malloc((nep + 6) * sizeof(char));
if(NULL != var1)
{
strncpy(var1, mystring+nep, (myindicator+nep+6));
var1[myindicator+nep+6] = '\0';
free(var1);

printf("Var 1: %s", var1);

nep = nep +myindicator+6;
}

getchar();
return 0;
}

最佳答案

我修复了一些东西,在评论中找到它。但是你需要查看C语言手册...!

int main()
{
char mystring[100];
char *stringID;
int nep;
// Changed to integer, not pointer to int.
int myindicator;
char *var1;

nep = 0;
printf("Please enter your CODE\n");

/*
This scanf is a bad idea for the same reason for which, below, we take
care to allocate memory enough for whatever we have to do.
Should someone input 250 characters in a buffer of size 100, those 150
extra characters would wreak havoc and possibly endanger the system.
*/
// scanf("%s", &mystring);
fgets(mystring, sizeof(mystring)-1, stdin);
// fgets will read at most "sizeof(mystring)-1", that is, 99 bytes,
// from "stdin" (STanDard INput), the same as scanf. But it will halt
// when reaching the limit given. It's up to us to give a "real" limit
// (nothing stops you from saying 15000 -- even if the true value is 100).

// C strings are made of characters, terminated by a zero byte.
// So you need 5 here, to store 4 characters
stringID = (char *)malloc(5 * sizeof(char));

if (NULL == stringID)
{
// Serious out of memory error: no sense going on.
// fprintf(stderr, "Out of memory\n");
abort();
}

strncpy(stringID, mystring, 4);
stringID[4] = '\0';

printf("ID: %s\n", stringID);

free(stringID);

nep = nep + 4;
printf("NEP: %d\n", nep);

// Now we want to decode the fifth digit.

// I use '0' as character. So if the fifth digit is '0', '0'-'0' will give 0
// and if it is '9', '9'-'0' will give 9 (the number).
// The trick does not work with more than one digit, of course.
myindicator = mystring[nep] - '0';

// Had I wanted to read 3 digits, I would have had to copy them into a
// temporary buffer, add a zero in the fourth position, then run atol()
// on the resulting buffer: atol("12345\0" /* A STRING */) = 12345 /* A NUMBER */;

printf("VLI : %d\n", myindicator);

// Copy "myindicator" bytes, so alloc myindicator+1 chars
var1 = (char *)malloc((myindicator + 1) * sizeof(char));

// Check that var1 is not null and abort if it is
if (NULL == var1)
abort();

strncpy(var1, mystring + 6, myindicator);
var1[myindicator+1] = '\0';

// Moved this printf before the free. See why below.
printf("Prefix : %s\n", var1);

// NEVER use a variable after you freed it!!!
// it might APPEAR to work, but will stab you in the back the first chance it gets.
// Good if paranoid habit: null a var as soon as you've freed it.
free(var1); var1 = NULL;

getchar();
return 0;
}

关于C语言: Newb translating code from javascript to C,代码包含malloc、strncpy、指针,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/11421444/

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