Why does the C system() function fail when parameters contain spaces?

C system() Function Malfunctions Due to Spaces in Parameters

When utilizing the system() function in C to execute a program with parameters containing spaces, it may result in an error regarding incorrect filename, directory name, or volume label syntax. This issue arises when both the executable's path and the parameter file path contain spaces.

For example:

<code class="cpp">#include <stdlib.h>
#include <conio.h>

int main() {
    system("\"C:\Users\Adam\Desktop\pdftotext\" -layout \"C:\Users\Adam\Desktop\week 4.pdf\"");
    _getch();
}</code>

In this code, the system() function attempts to execute the "pdftotext" executable with two parameters. However, the presence of spaces in both the executable path and the parameter path triggers the error.

Cause of the Issue

The system() function passes its arguments to the cmd /k command, which interprets the arguments according to specific rules. One of these rules states that if the command line contains exactly two quote characters, no special characters between the quotes, and the string is the name of an executable file, then the quote characters are preserved.

However, in the example code, the string between the quotes contains a space, violating the rule. Consequently, the cmd /k command interprets the string as an invalid executable name and produces the error.

Solution

To resolve this issue, enclose the entire command in additional quotes:

<code class="cpp">system("\"\"C:\Users\Adam\Desktop\pdftotext\" -layout \"C:\Users\Adam\Desktop\week 4.pdf\"\"");</code>

This ensures that the entire command string is parsed as one argument, preventing the cmd /k command from misinterpreting it.

Additionally, to guarantee that the string is always parsed by the correct rule, you can include the /S switch:

<code class="cpp">system("cmd /S /C \"\"C:\Users\Adam\Desktop\pdftotext\" -layout \"C:\Users\Adam\Desktop\week 4.pdf\"\"");</code>

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