c中的指針表達有什麼問題？

Question

我正在使用一個函數，該函數具有在qsort中用於比較以升序或取消順序排序的變量字段的段（如下所示）。我在NormalizeResClass函數中對氣體和油井分類進行了排序，並添加了第三個訂單（斷言爲0，下降爲1，第三個訂單爲2），該函數爲分類返回不同的int。

我添加了如下所示的(typsort == 2)的代碼，但只有在將保留類作爲唯一排序類型時才能正確排序。如果我按保留級別和名稱的順序排序，它就不會排序。

else塊中的原始代碼在xval和yval之前使用*((int *)，我在指針上很弱。我知道它是投射到int，但NormalizeResClass函數已經返回一個int，所以我不需要投射，如果我使用它，我得到一個segmentaion故障。

static char *Strings = NULL; // Global var 

int result= 0; // local var 
int ft; // local var 

// ft is checked before going to this to be >= 0 

if (typsort == 2) 
{ 
    // the code that I have added 
    result = strncmp (Strings + NormalizeResClass (xval), 
         Strings + NormalizeResClass (yval), ft); 
} 
else 
{ 
    // this code was there and the sorting was right 
    result = strncmp (Strings + *((int *) xval), 
         Strings + *((int *) yval), ft); 
} 

這是正常化功能如下我可能需要確保所有這些都有一個唯一的編號 幾個具有相同。

 
int NormalizeResClass (char rc)
 
{
 
    /
 
     Given a reserve class string , return a reserve class number.
 
    */
 

register int i;
 
    register char *p, *q;
 

static struct
 
    {
 
     int index;
 
     char str;
 } RCposs[] =
 {
 {
 1, "PROVED DEVELOPED PRODUCING"},
 {
 2, "PROVED PRODUCING SECONDARY"},
 {
 3, "PROVED PRODUCING TERTIARY"},
 {
 1, "PROVED PRODUCING"},
 {
 4, "PROVED SHUT-IN"},
 {
 5, "PROVED DEVELOPED NON-PRODUCING"},
 {
 5, "PROVED NON-PRODUCING"},
 {
 6, "PROVED DEVELOPED BEHIND-PIPE"},
 {
 6, "PROVED BEHIND-PIPE"},
 {
 8, "PROVED UNDEVELOPED SECONDARY"},
 {
 9, "PROVED UNDEVELOPED TERTIARY"},
 {
 7, "PROVED UNDEVELOPED"},
 {
 1, "PROVED"},
 {
 10, "PROBABLE DEVELOPED PRODUCING"},
 {
 11, "PROBABLE PRODUCING SECONDARY"},
 {
 12, "PROBABLE PRODUCING TERTIARY"},
 {
 13, "PROBABLE SHUT-IN"},
 {
 10, "PROBABLE PRODUCING"},
 {
 14, "PROBABLE DEVELOPED NON-PRODUCING"},
 {
 14, "PROBABLE NON-PRODUCING"},
 {
 15, "PROBABLE DEVELOPED BEHIND-PIPE"},
 {
 15, "PROBABLE BEHIND-PIPE"},
 {
 17, "PROBABLE UNDEVELOPED SECONDARY"},
 {
 18, "PROBABLE UNDEVELOPED TERTIARY"},
 {
 16, "PROBABLE UNDEVELOPED"},
 {
 20, "PROBABLE PRIMARY/SECONDARY"},
 {
 21, "PROBABLE SECONDARY"},
 {
 19, "PROBABLE"},
 {
 22, "POSSIBLE DEVELOPED PRODUCING"},
 {
 23, "POSSIBLE PRODUCING SECONDARY"},
 {
 24, "POSSIBLE PRODUCING TERTIARY"},
 {
 25, "POSSIBLE SHUT-IN"},
 {
 22, "POSSIBLE PRODUCING"},
 {
 26, "POSSIBLE DEVELOPED NON-PRODUCING"},
 {
 26, "POSSIBLE NON-PRODUCING"},
 {
 27, "POSSIBLE DEVELOPED BEHIND-PIPE"},
 {
 27, "POSSIBLE BEHIND-PIPE"},
 {
 29, "POSSIBLE UNDEVELOPED SECONDARY"},
 {
 30, "POSSIBLE UNDEVELOPED TERTIARY"},
 {
 28, "POSSIBLE UNDEVELOPED"},
 {
 22, "POSSIBLE"},
 {
 32, "PROSPECTIVE PRIMARY/SECONDARY"},
 {
 33, "PROSPECTIVE SECONDARY"},
 {
 31, "PROSPECTIVE"},
 {
 34, "ANALOGY"},
 {
 35, "DEPLETE"},
 {
 36, "PROV+PROB+POSS UNDEVELOPED RESERVES"},
 {
 37, "PROV+PROB+POSS DEVELOPED RESERVES"},
 {
 38, "PROV+POSS UNDEVELOPED RESERVES"},
 {
 39, "PROV+POSS DEVELOPED RESERVES"},
 {
 40, "PROB+POSS UNDEVELOPED RESERVES"},
 {
 41, "PROB+POSS DEVELOPED RESERVES"},
 {
 42, "PROV+PROB UNDEVELOPED RESERVES"},
 {
 43, "PROV+PROB DEVELOPED RESERVES"},
 {
 44, "RISKED PROV UNDEVELOPED RESERVES"},
 {
 45, "RISKED PROB UNDEVELOPED RESERVES"},
 {
 46, "RISKED POSS UNDEVELOPED RESERVES"},
 {
 47, "RISKED PROV BEHIND-PIPE RESERVES"},
 {
 48, "RISKED PROB BEHIND-PIPE RESERVES"},
 {
 49, "RISKED POSS BEHIND-PIPE RESERVES"},
 {
 50, "PLANT PRODUCTS SALES"},
 {
 51, "PROBABLE PLANT PRODUCTS SALES"},
 {
 52, "POSSIBLE PLANT PRODUCTS SALES"},
 {
 53, "POTENTIAL PLANT PRODUCTS SALES"},
 {
 54, "PROVED GAS PIPELINE SALES"},
 {
 55, "PROBABLE GAS PIPELINE SALES"},
 {
 56, "POSSIBLE GAS PIPELINE SALES"},
 {
 57, "POTENTIAL GAS PIPELINE SALES"},
 {
 58, "PROVED OIL PIPELINE SALES"},
 {
 59, "PROBABLE OIL PIPELINE SALES"},
 {
 60, "POSSIBLE OIL PIPELINE SALES"},
 {
 61, "POTENTIAL OIL PIPELINE SALES"},
 {
 0, NULL / terminator */ }};
 

for (i = 0; (q = RCposs[i].str); i++)  
    { 
     p = rc; 
     while (*p++ == *q++) 
      { 
       if ((*q == '\0')) 
        return RCposs[i].index; 
      } 
    } 
return (0); 

}

Answer 1

根據您所顯示的代碼，它看起來像全球Strings變量是一個大的內存塊中包含許多不同的字符串（每記錄一個，想必）。

原始代碼：

result = strncmp (Strings + *((int *) xval), 
        Strings + *((int *) yval), ft); 

在Strings[xval]在Strings[yval]字符串進行比較的字符串，具有最大長度ft。

我不知道NormalizeResClass(x)函數做什麼，但如果是去工作的以類似的方式對舊代碼，它需要返回一個int表示在一個字符串的開頭位置Strings內存塊。它必須而不是返回的索引將落在該內存塊之外，否則調用strncmp將從誰知道哪裏開始讀取。

更新：

它看起來像你的NormalizeResClass函數返回一個整數排名資源類的字符串。在這種情況下，您應該使用strncmp()和Strings[]，而不是而不是。代碼應該是這樣的：

if (typsort == 2) 
{ 
    int xRank = NormalizeResClass (xval); 
    int yRank = NormalizeResClass (yval); 
    if (xRank == yRank) { result = 0; } 
    else if (xRank > yRank) { result = 1; } 
    else if (xRank < yRank) { result = -1; } 
}