如何將char數組轉換爲整數元素？

Question

我有一個大小爲30的字符數組（char array [30]）。它只有一個整數據類型的元素。我如何將該數組元素轉換爲C中的整數元素？

任何幫助將不勝感激！

Answer 1

如果我理解正確你的問題：

#include <stdio.h> 

int main() 
{ 
    int i = atoi(" 3 "); 
    printf("%d", i); 
    return 0; 
} 

atoi將忽略任何空白，直到它找到一個數字，當它檢測到一個非數字字符就會停止。

Demo

Answer 2

的評論說，幾乎一切，給你詳細介紹有關atoi，sscanf和strtol。這裏我有一些示例字符串和這些函數返回的結果。因爲不是每個字符串都轉換成功我添加了一個擴展實現strtol下面這個。生成此輸出的代碼也在下面給出see it online in action at ideone。

1. 的atoi：字符串與非編號開始進行評估，以0。根本沒有錯誤信息。

   0: atoi with "3"  to integer: +3 
   1: atoi with " 3 " to integer: +3 
   2: atoi with " -3 " to integer: -3 
   3: atoi with "str 3 " to integer: +0 
   4: atoi with "str-3 " to integer: +0 
   5: atoi with " 3str" to integer: +3 
   6: atoi with " -3str" to integer: -3 
   7: atoi with "str-3str" to integer: +0 
   8: atoi with "s-r-3str" to integer: +0 
   

2. sscanf的：與%d就叫：同樣在這裏，但返回匹配的項目作爲計數，所以0將指示錯誤。

   0: sscanf with "3"   to integer: +3 | itemCount = 1 
   1: sscanf with " 3 " to integer: +3 | itemCount = 1 
   2: sscanf with " -3 " to integer: -3 | itemCount = 1 
   3: sscanf with "str 3 " to integer: +0 | itemCount = 0 --> Error! 
   4: sscanf with "str-3 " to integer: +0 | itemCount = 0 --> Error! 
   5: sscanf with " 3str" to integer: +3 | itemCount = 1 
   6: sscanf with " -3str" to integer: -3 | itemCount = 1 
   7: sscanf with "str-3str" to integer: +0 | itemCount = 0 --> Error! 
   8: sscanf with "s-r-3str" to integer: +0 | itemCount = 0 --> Error! 
   

3. 與strtol：同樣在這裏，但返回錯誤代碼爲errno的範圍溢出。另外endPtr是爲您提供有關轉換的更多詳細信息的參數之一。

   0: strtol with "3"   to integer: +3 | errno = 0, StartPtr = 0x7ffc47e9a140, EndPtr = 0x7ffc47e9a141, PtrDiff = 1 
   1: strtol with " 3 " to integer: +3 | errno = 0, StartPtr = 0x7ffc47e9a130, EndPtr = 0x7ffc47e9a135, PtrDiff = 5 
   2: strtol with " -3 " to integer: -3 | errno = 0, StartPtr = 0x7ffc47e9a120, EndPtr = 0x7ffc47e9a125, PtrDiff = 5 
   3: strtol with "str 3 " to integer: +0 | errno = 0, StartPtr = 0x7ffc47e9a110, EndPtr = 0x7ffc47e9a110, PtrDiff = 0 --> Error! 
   4: strtol with "str-3 " to integer: +0 | errno = 0, StartPtr = 0x7ffc47e9a100, EndPtr = 0x7ffc47e9a100, PtrDiff = 0 --> Error! 
   5: strtol with " 3str" to integer: +3 | errno = 0, StartPtr = 0x7ffc47e9a0f0, EndPtr = 0x7ffc47e9a0f5, PtrDiff = 5 
   6: strtol with " -3str" to integer: -3 | errno = 0, StartPtr = 0x7ffc47e9a0e0, EndPtr = 0x7ffc47e9a0e5, PtrDiff = 5 
   7: strtol with "str-3str" to integer: +0 | errno = 0, StartPtr = 0x7ffc47e9a0d0, EndPtr = 0x7ffc47e9a0d0, PtrDiff = 0 --> Error! 
   8: strtol with "s-r-3str" to integer: +0 | errno = 0, StartPtr = 0x7ffc47e9a0c0, EndPtr = 0x7ffc47e9a0c0, PtrDiff = 0 --> Error! 
   

這裏是我的strtol函數的代碼，這樣就可以解析更多不同的字符串。 my_strtol的用法與strtol完全相同。如果你有如下字符串，還有一個幫助函數："str-str-3"，因爲第一個減號-不是整數。

my_strtol（）實現：

/* Position exactly to integer beginning */ 
/* e.g. if you have: "str-str-3str "  */ 
/* the returning pointer will point to: */ 
/* "-3str".        */ 
const char* getNumberPos(const char* str) 
{ 
    const char* curChar = str; 
    /* Iterate through part of integer is there. */ 
    while ( '\0' != curChar 
      && !(isdigit(*curChar) || '+' == *curChar || '-' == *curChar)) 
    { 
     ++curChar; 
    } 
    /* Check if the sign is part of an integer, */ 
    /* if not use this function recursive!  */ 
    if ('+' == *curChar || '-' == *curChar) 
    { 
     const char* nextChar = curChar + 1; 
     if ( '\0' != *nextChar 
      && !isdigit(*nextChar)) 
     { 
     ++curChar; 
     curChar = getNumberPos(curChar); 
     } 
    } 
    return curChar; 
} 

/* Extended strtol function */ 
long my_strtol(const char* str, char** endptr, int base) 
{ 
    const char* curChar = getNumberPos(str); 
    return strtol(curChar, endptr, base); 
} 

my_strtol的結果：的my_strtol功能與上面給出的所有字符串的工作原理：

0: my_strtol with "3"   to integer: +3 | errno = 0, StartPtr = 0x7ffc47e9a140, EndPtr = 0x7ffc47e9a141, PtrDiff = 1 
1: my_strtol with " 3 " to integer: +3 | errno = 0, StartPtr = 0x7ffc47e9a130, EndPtr = 0x7ffc47e9a135, PtrDiff = 5 
2: my_strtol with " -3 " to integer: -3 | errno = 0, StartPtr = 0x7ffc47e9a120, EndPtr = 0x7ffc47e9a125, PtrDiff = 5 
3: my_strtol with "str 3 " to integer: +3 | errno = 0, StartPtr = 0x7ffc47e9a110, EndPtr = 0x7ffc47e9a115, PtrDiff = 5 
4: my_strtol with "str-3 " to integer: -3 | errno = 0, StartPtr = 0x7ffc47e9a100, EndPtr = 0x7ffc47e9a105, PtrDiff = 5 
5: my_strtol with " 3str" to integer: +3 | errno = 0, StartPtr = 0x7ffc47e9a0f0, EndPtr = 0x7ffc47e9a0f5, PtrDiff = 5 
6: my_strtol with " -3str" to integer: -3 | errno = 0, StartPtr = 0x7ffc47e9a0e0, EndPtr = 0x7ffc47e9a0e5, PtrDiff = 5 
7: my_strtol with "str-3str" to integer: -3 | errno = 0, StartPtr = 0x7ffc47e9a0d0, EndPtr = 0x7ffc47e9a0d5, PtrDiff = 5 
8: my_strtol with "s-r-3str" to integer: -3 | errno = 0, StartPtr = 0x7ffc47e9a0c0, EndPtr = 0x7ffc47e9a0c5, PtrDiff = 5 

下面的代碼顯示的是測試代碼爲所有四個功能生成輸出。

#include <stdio.h> 
#include <stdlib.h> 
#include <stddef.h> 
#include <ctype.h> 
#include <string.h> 
#include <errno.h> 

int main() 
{ 
    /* Loop index */ 
    int idx; 

    /* Declare and initialize char arrays. */ 
    char array[]  = { "3" }; 
    char arrayI[]  = { " 3 " }; 
    char arrayII[] = { " -3 " }; 
    char arrayIII[] = { "str 3 " }; 
    char arrayIV[] = { "str-3 " }; 
    char arrayV[]  = { " 3str" }; 
    char arrayVI[] = { " -3str" }; 
    char arrayVII[] = { "str-3str" }; 
    char arrayVIII[] = { "s-r-3str" }; 

    /* Save each array in one array for iteration purposes. */ 
    const char* const arrays[] = { array, 
            arrayI, 
            arrayII, 
            arrayIII, 
            arrayIV, 
            arrayV, 
            arrayVI, 
            arrayVII, 
            arrayVIII }; 
    /* Get size of that array. */ 
    const int arraysSize = sizeof(arrays)/sizeof(char*); 

    /* atoi(): Does not detect errors! */ 
    for (idx = 0; idx < arraysSize; ++idx) 
    { 
     int integer = atoi(arrays[idx]); 

     printf("%d: atoi with \"%s\" %*s to integer: %+d\n", 
      idx, 
      arrays[idx], 
      8 - strlen (arrays[idx]), 
      "", 
      integer); 
    } 
    printf("\n"); 

    /* sscanf(): Error detection by using the matched item count. */ 
    for (idx = 0; idx < arraysSize; ++idx) 
    { 
     int integer = 0; 
     int itemCount = sscanf(arrays[idx], "%d", &integer); 

     printf("%d: sscanf with \"%s\" %*s to integer: %+d | itemCount = %d", 
      idx, 
      arrays[idx], 
      8 - strlen (arrays[idx]), 
      "", 
      integer, 
      itemCount); 

     if (0 == itemCount) 
     { 
     printf(" --> Error!"); 
     } 
     printf("\n"); 
    } 
    printf("\n"); 

    /* strtol(): Error detection by using errno and returned end pointer. */ 
    for (idx = 0; idx < arraysSize; ++idx) 
    { 
     char*  endPtr = NULL; 
     ptrdiff_t ptrDiff = 0; 
     errno    = 0; 
     /* You have to check if the long can be stored in the int, not done here! */ 
     int integer = (int) strtol(arrays[idx], &endPtr, 10); 
     ptrDiff = endPtr - arrays[idx]; 

     printf("%d: strtol with \"%s\" %*s to integer: %+d | errno = %d, StartPtr = %p, EndPtr = %p, PtrDiff = %ld", 
      idx, 
      arrays[idx], 
      8 - strlen (arrays[idx]), 
      "", 
      integer, 
      errno, 
      (void*) arrays[idx], 
      (void*) endPtr, 
      ptrDiff); 

     if (0 != errno || 0 == ptrDiff) 
     { 
     printf(" --> Error!"); 
     } 
     printf("\n"); 
    } 
    printf("\n"); 

    /* my_strtol: Same as strtol here. */ 
    for (idx = 0; idx < arraysSize; ++idx) 
    { 
     char*  endPtr = NULL; 
     ptrdiff_t ptrDiff = 0; 
     errno    = 0; 
     /* You have to check if the long can be stored in the int, not done here! */ 
     int integer = (int) my_strtol(arrays[idx], &endPtr, 10); 
     ptrDiff = endPtr - arrays[idx]; 

     printf("%d: my_strtol with \"%s\" %*s to integer: %+d | errno = %d, StartPtr = %p, EndPtr = %p, PtrDiff = %ld", 
      idx, 
      arrays[idx], 
      8 - strlen (arrays[idx]), 
      "", 
      integer, 
      errno, 
      (void*) arrays[idx], 
      (void*) endPtr, 
      ptrDiff); 

     if (0 != errno || 0 == ptrDiff) 
     { 
     printf(" --> Error!"); 
     } 
     printf("\n"); 
    } 

    return 0; 
}