從int函數返回char *而不使用指針？

Question

我有一個函數，從給定的文件中讀取，查找給定的關鍵字，返回一個由給定字符串與單詞分離的keyvalue。 我的函數返回值現在是char *，就我的理解而言，這是錯誤處理的欠佳值。 另一方面，我不會用指針來存儲值的指針。至少在這種情況下。

有沒有辦法通過函數返回字符串值，而返回int值成功/失敗？

我的char *代碼：

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 

/*! 
* @brief Loads the config file and returns value of requested parameter search 
* @param char *file - Config file to search in 
* @param char *seperator - Seperator to identify keyword and keyvalue 
* @param char *search - Requested parameter to look for 
* @return char * - Value of found keyword or error if search failed 
*/ 

int confin(char *file, char *seperator, char *search) 
{ 
    FILE *conf; 
    char *buffer; 
    char *output; 
    char line[256]; 

    char *returnerror = "Error!"; 


    if((conf = fopen(file, "r")) == NULL)         // Try to open file from path, return error if failed 
    { 
     fprintf(stderr, "Could not open config file \"%s\"!\n", file); 
     return returnerror; 
    } 

    while (fgets(line, sizeof(line), conf) != NULL)       // Read lines of file until the end is reached 
    { 
     buffer = strtok(line, seperator);         // Search for first appearance of seperator in line; 
     if((strcmp(buffer,search)) == 0)         // If keyword is found, 
     { 
      buffer = strtok(NULL, seperator);        // buffer the keyvalue, 
      output = malloc(sizeof(buffer)); 
      strcpy(output, buffer);           // copy it into the output string, 
      output[strcspn(output, "\n")] = 0;        // replace the "\n" char from the end with terminating 0 
      fclose(conf); 
      return output;             // and return the value of output.   
     } 
    } 

    fprintf(stderr, "Could not find config keyword \"%s\"!\n", search); 
    fclose(conf); 
    return returnerror; 

} 


int main() 
{ 
    printf("%s\n",confin("test.conf","=","test")); 
} 

我嘗試下面的代碼，但返回的值（NULL）

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 

/*! 
* @brief Loads the config file and returns value of requested parameter search 
* @param char *file - Config file to search in 
* @param char *seperator - Seperator to identify keyword and keyvalue 
* @param char *search - Requested parameter to look for 
* @return int - 0 on success, 1 on failure 
*/ 

int confin(char *file, char *seperator, char *search, char *value) 
{ 
    FILE *conf; 

    char *output; 
    char *buffer; 
    char line[256]; 


    if((conf = fopen(file, "r")) == NULL)         // Try to open file from path, return error if failed 
    { 
     fprintf(stderr, "Could not open config file \"%s\"!\n", file); 
     return 1; 
    } 

    while (fgets(line, sizeof(line), conf) != NULL)       // Read lines of file until the end is reached 
    { 
     buffer = strtok(line, seperator);         // Search for first appearance of seperator in line; 
     if((strcmp(buffer,search)) == 0)         // If keyword is found, 
     { 
      buffer = strtok(NULL, seperator);        // buffer the keyvalue, 
      output = malloc(sizeof(buffer)); 
      strcpy(output, buffer);           // copy it into the output string, 
      output[strcspn(output, "\n")] = 0;        // replace the "\n" char from the end with terminating 0. 
      strcpy(value,output);           // Store the new value in my return value  
      fclose(conf); 
      free (output); 
      return 0;              // and return the value of output.   
     } 
    } 

    fprintf(stderr, "Could not find config keyword \"%s\"!\n", search); 
    fclose(conf); 
    return 1; 

} 


int main() 
{ 
    char value[256] = "\0"; 
    printf("%s\n",confin("test.conf","=","test",value)); 
} 

希望這件事被整理出來快。即使這意味着我必須在最後使用指針方法。提前致謝！

Answer 1

變化：

int main() 
{ 
    char value[256] = "\0"; 
    printf("%s\n",confin("test.conf","=","test",value)); 
} 

到：

int main() 
{ 
    char value[256] = "\0"; 
    int retval = confin("test.conf","=","test",value); 
    if(retval) 
     // some error handling 
    printf("%s\n", value); 
} 

你做了什麼是呼叫confin，其分配的字符串值value，但是你想從這個函數打印返回int（如一個字符串）而不是value。

您也可以直接返回char*，如果密鑰不在您的配置文件中，則返回NULL。這僅僅是「沒有這樣的關鍵」類型錯誤的簡單情況。在這種情況下，您只需檢查confin是否返回NULL。

Answer 2

你已經有了一些很好的答案，但我很驚訝沒有人提到這裏的errno。 （https://en.wikipedia.org/wiki/Errno.h）

Errno是C管理錯誤的常用方法之一。例如你可以在發生錯誤的函數中自己設置errno並返回NULL。這將通知調用函數出錯。