从C中的函数返回一个字符串 [英] Returning a string from a function in C

问题描述

我有我想返回一个字符串C函数。

如果我打印返回前，然后我看到croc_data_0186.idx字符串

如果我尝试和打印则返回我看到croc_data_á☼字符串

有人能看到我在做什么错了？

问题的功能：

 的char * getSegmentFileName（FILE *文件，诠释linelength个，INT行号）
{
    字符* fileNameString;    fseek的（文件，行号* linelength个，SEEK_SET）;    焦线[linelength个]
    与fgets（行，linelength个，文件）;    字符* lineElements [3];
    lineElements [0] = strtok的（行，：）;
    lineElements [1] = strtok的（NULL，：）;
    lineElements [2] = strtok的（NULL，：）;    fileNameString = lineElements [2];    的printf（getSegmentFileName fileNameString是：％S \\ r \\ n，fileNameString）;    返回fileNameString;
}
 

调用code：

  INT indexSearch（FILE *文件的char *值，INT低，诠释高，字符* segmentFileName）
{
    ...    segmentFileName = getSegmentFileName（文件，linelength个，中旬）;
    的printf（indexSearch：segmentFilename3是：％S \\ r \\ n，segmentFileName）;    ...
}
 

解决方案

您正在返回一个指向本地数据，这是不是在函数返回后有效。你必须合理分配字符串。

这既可以在调用函数来完成，通过提供一个缓冲到被调用的功能，并将其复制字符串到提供的缓冲区。像这样的：

 字符segmentFileName [SOME_SIZE]
getSegmentFileName（文件，linelength个，中旬，segmentFileName）;
 

和 getSegmentFileName 功能：

 无效getSegmentFileName（FILE *文件，诠释linelength个，诠释LINENUMBER，字符* segmentFileName）
{
    / * ... * /    的strcpy（segmentFileName，fileNameString）;
}
 

另外一个解决办法是分配字符串内存在 getSegmentFileName ：

 的strdup回报（fileNameString）;
 

但你要记住免费字符串后面。

I have a c function that I want to return a string.

If I print the string before it is returned then I see croc_data_0186.idx

If I try and print the string that is returned then I see croc_data_á☼

Can anyone see what I am doing wrong?

Problem function:

char* getSegmentFileName(FILE *file, int lineLength, int lineNumber)
{
    char* fileNameString;

    fseek(file, lineNumber * lineLength, SEEK_SET);

    char line[lineLength];
    fgets(line, lineLength, file);

    char *lineElements[3];
    lineElements[0] = strtok(line, ":");
    lineElements[1] = strtok(NULL, ":");
    lineElements[2] = strtok(NULL, ":");

    fileNameString = lineElements[2];

    printf ("getSegmentFileName fileNameString is: %s \r\n", fileNameString);

    return fileNameString;
}

Calling code:

int indexSearch(FILE *file, char* value, int low, int high, char* segmentFileName)
{
    ...

    segmentFileName = getSegmentFileName(file, lineLength, mid);
    printf ("indexSearch: segmentFilename3 is: %s \r\n", segmentFileName);

    ...
}

解决方案

You are returning a pointer to local data, which is not valid after the function returns. You have to allocate the string properly.

This can be done in either the calling function, by supplying a buffer to the called function, and it copies the string over to the supplied buffer. Like this:

char segmentFileName[SOME_SIZE];
getSegmentFileName(file, lineLength, mid, segmentFileName);

and the getSegmentFileName function:

void getSegmentFileName(FILE *file, int lineLength, int lineNumber, char *segmentFileName)
{
    /* ... */

    strcpy(segmentFileName, fileNameString);
}

The other solution is to allocate the memory for the string in getSegmentFileName:

return strdup(fileNameString);

but then you have to remember to free the string later.

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